In order to get Manaphy in Pokemon Diamond and Pearl, you will need to have Pokemon Ranger. Once you have beaten the game go to ranger net at the Main Menu.

The screen will then say "Play a Special Mission". Press the X Button, the right shoulder button, and left on the directional pad. The screen should then say "Enter the password has been added".

Tap the touch screen and the game will save. If you tap the screen after the game saves a menu will appear called "Enter the password".

Tap on the menu and then enter the password. The password is:
P8M2--9D6F--43H7

You'll see a message that the password was accepted. Turn of the game and then turn it back on.

Go to Ranger net again and tap "Play a Special Mission". Select the mission "Recover the Precious Egg".

Defeat the mission and get the Manaphy Egg. You won't be able to hatch it until you get it on Diamond and Pearl.


I hope this helped!