The password for Manaphy in Ranger is:
P8M2 -- 9D6F -- 43H7
What do I have to do before I can input the password?
Before you can do the Manaphy mission, you just have to beat the Ranger story mode, unlocking the Ranger Net option.
How do I put in the password?
Here's the text from the official site:
1. Access Ranger Net after finishing the game. When you see Ranger Net on your main menu, click on it.
2. Your screen will show "Play a special mission." On your Nintendo DS, press the top Right trigger, the X button, and left on your directional pad simultaneously.
3. You should see a screen that says "Enter the password has been added."
4. Tap the touch screen, and wait as the game saves.
5. After the game saves, tap the screen again, and a new menu will come up that says "Enter the password."
6. When you click on the password menu, you'll be allowed to enter the password!