Enter +FOODSTAMPS+ as a code.

Enter CHACHING as a code.

Enter FITS as a code.

Enter WHATEXIT as a code.

Select "Options" at the main menu, then choose "Player Profile". Select the "Cheats" option, then enter one of the following case-sensitive codes.

Unlock Everything
Enter the follow password !SLACKER! at the password screen

Credits
Enter +FOODSTAMPS+ for 10,000 credits at a time.
This will eventually give you the credits to unlock the Fury bike that the first code does not.

Enter ALLQUIKI as a code.
Have a saved game file from ATV Offroad Fury 2 on your memory card.

If another rider comes up beside you, you can easily knock him off his ATV by performing a Bicycle (R2 + Left or Right) to raise your tires into his or her face.

Enter single player mode. Successfully complete the training course with a "Bronze" average.
Enter single player mode. Successfully complete the training course with a "Silver" average.
Enter single player mode. Successfully complete the training course with a "Gold" average.