Here’s how to get Manaphy!
Get on Pokemon Ranger and access Ranger Net.(you must beat the game to get this) Leave the screen on Play a special mission and then hold down the buttons, X, R, and the Dpad Left. You should see a popup on your screen saying you can now access enter the Password. Then click enter the password and enter the code: P8M2-9D6F-43H7
You have now unlocked the Secret Ranger Net Mission Rescue the Manaphy Egg! This is a pretty easy mission, it just takes a while. After you have beaten it, you find a button saying check the egg. Then click Send the egg.(or something like that) Now you must have another DS for this, and you must own Pokemon Pearl to hatch the egg because you cannot hatch eggs in the Fiore Region. Now on the other DS, stay on the Pokemon Pearl title screen. Once you have clicked send the egg on Ranger, then you should get something on Pearl, then follow the instructions. Once you have completed it, go to the nearest Pokemart and pick up your egg by talking to the guy standing in front of the counter. The egg will hatch soon! (manaphy’s only level 1 though!)
~(This was from Emtek77, coz i dont have pearl/ranger, just diamond. Her site is in my blogroll if you wanna check it out: www.clubpenguinnewspaperstand.wordpress.com)