The Basics
Let's get one thing straight. I do not bridge, standby, or mod in matchmaking so don't ask me to.
This page is now fully updated with my crazy cool modding knowlege!! 
MODDING: When you modify your xbox to make it do things that normally aren't possible in the regular game. Ex: In Halo 2 you can make a warthog fly, have a scarab in multiplayer, and many weapon variations.
There are 3 types of modding:
Action Replay Mods: These are the only mods that will not get you banned (unless noted otherwise by the uploader). These are either modded campaign saves or special gametype mods. You will need an AR Set found on Ebay. To do AR modding is simple. Install the program onto your computer using the disk. Then put the memory card into the memory card to USB cable. Then download a pre-saved game or one from www.codejunkies.com and then transfer it to your memory card. Then copy it to your xbox hardrive.
Softmodding: When you go to a website and download mods to your xbox.
Hardmodding: When you physically dismantle your xbox and insert a mod chip. You then program it and/ or download mods.
Sorry wanna-be modders but I don't know how to hardmod so don't ask me!!
NOTE: I do not recomend modding if you are easily frustrated or a complete n00b. Modding WILL get you banned from matchmaking and possibly xbox live. All mods carry the risk of deleting data on your hardrive or completely frying your xbox. Therefore it is best to backup your hardrive. Attempt at your own risk.
Softmodding can be very difficult. If you ever need help visit my contacts page.
If you wish to keep your original gamertag unbanned and want to sacrifice one for modding you will need something. Another xbox. If you sign onto live on your non-modded account they will still ban you, unless you take off the modded files. But this is a pain in the a-hole to do. I recomend to just find a friend and buy another xbox off them. NOTE: If you are a 2-month modder and have created multiple modding accounts there is a catch. If you create a lot of modding accounts Bungie can ban you completely from making any other accounts. They can do this by noticing that all your GT's had the same IP address or credit card #.
How to Softmod
So you want to softmod eh? Well here is a complete tutorial on how to do so.
Part I: Installing the program.
Alright to start off you must have an Action Replay and a copy of 007 Agent Under Fire, Mechassault, or Splinter Cell (Original). Alright get a LINUX file and a LINUX installer and copy them to your xbox (keep them in ZIP form). NOTE: Make sure all other game saves of your game are deleted. Then put in the game of choice and let it load. Press start game and choose the profile entitled LINUX. Then press checkpoints or something along those lines. Your screen will go dark then come up again a few seconds later. Depending on which installer you use your screen make look different. You must backup your MS dashboard and then backup your eeprom. After this is completed then go to install softmod. You should get a number of different options. Choose any one. There are 2 that you can download. EvolutionX and UnleashedX. Each have their own pro's and won't matter when you start softmodding. I recomend EvoX, it is less likely to srew up your xbox. After the program is installed then turn off your xbox. When you turn it back on you will be ready.
Part II: The Programs and You.
Alright now this is where you learn exactly how to transport your softmods. First of all make sure your xbox is connected directly to your computer. In the modded dashboard it should say what your IP address is. Write it down. Now after you have FlashFXP installed open it up. Ignore the trial details and come to the main screen. You will see a box on the left and right and a small one in the bottom left. Now press the lighting bolt in the middle. Enter your IP address and then for username and password just type xbox. If done correctly you will see in the right 7 folders entitled CDEFXYZ. These are all of your xbox's hardrive folders. To break it down: D drive is the DVD drive. E is the main place for saving. F and X should be empty. If you are in your modded dashboard go to system management. If you wish to go to your microsoft dashboard click M$ dashboard. Then click on system settings. You will see lot's of data facts about your hardrive. If you scroll down you will see your drives. E should have the most amount of space. Now keep in your modded dashboard. When you are connected to your xbox using FlashFXP this is the only time you can modify it. Alright now put in your copy of Halo 2 but don't play it. IMPORTANT: Before we proceed I recomend copying all of your xbox hardrive's folders to your computer. If your xbox crashes, vital system information could be lost. Alright go into the D drive. You will see many folders. You will need to copy these folders to your hardrive. You will not need to copy the folder labeled 'bink'. These are intro videos. To conserve space to save other games to the hardrive say Halo, you will need a lot of space. Also in the 'maps' folder you will not need to copy the campaign missions. These are some monster files and only take up unneccessary space. Copy all the other files to your computer hardrive. Highlight them and hit transfer. If you wish you can copy Halo as well. Just as before don't copy the 'bink' folder. Then after that is done go to your E and make a folder named 'games'. Then in there make a folder named 'Halo 2' and 'Halo' if you want. Then transfer all the files to the appropriate game folder. Now after these are copied go to your EvoX dashboard and go to the games on hd. Click Halo or Halo2. If all is well then it will say loading then you will get the main menu. Congrats now you can officially start to mod. Why did we do this you ask? Well you cannot mod permanent files on your disk. You must copy it and then it will allow you to modify it. An exception would be this. In Halo 2 if you downloaded the new maps then go to the E drive and hit TDATA. Click on the 4d530064 or something like that then click on $c. Then you will see 3 folders, the 3 map downloads. These new maps you will not need to copy. You can modify then as is. NOTE: When you have modified maps on your hd the only way to play them is when you play them with no disk off the hd. If you want to play the map like normal simply put in a disk.
Part III: Modifying your maps.
Now if you look at your map folders you'll notice the names of maps Ex: containment.map. deltatap is sanctuary, triplicate is terminal and dune is relic. Now when you find mods on the net you will need to now the extension. If it is in .map file then this is as easy as it gets. Go into FlashFXP and find the saved .map file on your hardrive. Replace it with the same map on the xbox hardrive. To connect you must be the modded dash. Make sure the name is the EXACT same. After it is replaced turn off your xbox and then turn it back on. Load the game and bang your map is modded. Now that was easy but most of the mods you will find will be in patches. These are mods that are applied to the map to mod them. If you find a .ppf file then open up dothalo. Click open map and load the map you want to mod. NOTE: You must download your map from your hardrive to your computer. Then load it into the patch program. After the map is loaded then press apply .ppf patch. Browse your computer to find the the patch you want. Then hit apply patch. After this is done press fix encryption. Then in the tags window hit save changes. If an error message cccurs just press continue. Now you map will be modded. Load it your xbox. The 2nd file is .sppf or super .ppf. To do this open the sppf program. Load the map and then browse for the patch. Then hit apply. Then open the encryption program. Find the map and press ok. After it is encrypted you can transport it to your hardrive. The 3rd type is Serenity. This is less common but still useful to know.First off download a serenity pactch. WinZip or UnRAR the file. Find the .serenity file in the folder(s). Once you've found it remember the location. Open up serenity and click the apply tab.
Now click the first box with 3 periods and find the patch and open it. Now for the source map click the box on the right side of it and search for the original map.(for the patch. ex.Coagulation For the output map search for the map that you want the patch to be applied too.Click Generate Patch. Now transport it to your xbox. With these steps you can download practically any mods.
NOTES:
After you have applied a patch to a level you cannot add another one. You must have a blank or clean map to mod.
Old maps are just as easy to mod as new ones. Just download them to your hd and you can mod them.
Some very hardmodded maps or skinned maps may not be playable by other people on live. Also most of the time the skins can only be viewed by you.
I do not know how to create your own mods. (Yet!)
There are 2 types of softmods (sorta).
1. Matchmaking Mods: These are patches you apply to each map. Ex: Run fast, jump high, 360 aim, etc. These will be activated for the modder only whenever you are on a level that has that patch. These normally only work for new maps.
2. Custom Game Mods: These are mods that will only work when the modder loads a map that has mods. Most of these mods will work with the common people who don't have mods. These will only activate in custom games and as soon as the modder leaves, will no longer work.
These 2 mods, to my knowledge, cannot be combined. You must apply them at seperate times.
Downloads
PROGRAMS:
LINUX Installer: http://us.codejunkies.com/saves_show_game.asp?c=US&cr=USD&cs=$&r=0&l=1&g=559437140&p=8
LINUX Game Saves: http://us.codejunkies.com/saves.asp?c=US&cr=USD&cs=$&r=0&l=1
To find a game save just go to the game you need. Then find a save named 'Linux'
WinZip: http://www.winzip.com/downse.htm
WinRAR: http://www.rarlab.com/download.htm
FlashFXP: http://www.download.com/FlashFXP/3000-2160-10037696.html?part=dl-FlashFXP&subj=dl&tag=button
Dot Halo: http://www.halomaps.com/dothalo.html
SPPF: http://forums.halomods.com/viewtopic.php?t=35059
You must become a member to download.
Encryptomatic Signature: http://www.halomaps.com/encryptomatic-signature.html
These are all the programs you will need to softmod.
TUTORIALS:
http://www.techfreaks.org/articles/modxbox.shtml
http://forums.afterdawn.com/thread_view.cfm/337897
http://forums.halomods.com/viewtopic.php?t=36840
EXCELLENT MODS:
36 Containment Skytracks!!: http://www.se7ensins.com/forums/map-packs/32233-racetrack-pack-36-tracks-plus-source-patch.html
Matchmaking Mods: http://www.freewebs.com/omegax1/MatchMaking PPF.rar
Relic, Turf, and Sanctuary Mods: http://www.strategyinformer.com/dlredir.php?id=Ds9IxQ3cST29rB%2FGgRymLA%3D%3D
Kick Ass Turf: http://www.assassin4hire.com/upload/details.php?file=214
Sick Ascension Mod!!: http://forums.halomods.com/viewtopic.php?t=55057 (Must be a member)
Awesome Airstrike Mod!! http://forums.halomods.com/viewtopic.php?t=17631 (Must be a member)
These are only a SMALL fraction of working mods that I have found and tried.
WEBSITES:
http://www.strategyinformer.com/pc/mods/halo2/mod.html
Of course there are many more websites and mods to go find. So pop up Google and go a hunting!!!
Etc.
BRIDGING: When a person makes the game give host to a specific person. Host usually has a little of an advantage (especially with shotgun) and is needed for standbying and modding. To check if you're host, at the beginning of the game hold the back button. If you don't have a red X by your name then you're host.
STANDBYING: You know when your playing a game and then you go to that annoying blue screen? Well that's either standbying or someone quitting with a bad connection. With standbying one person removes their connection which causes everyone else to get a blue screen. Then the person or team is free to go around the map and get free kills. If your trying to kill someone but they're just walking into walls not getting affected then their standbying. You won't kill them, then you'll blue screen, then you'll come out dead.
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