Enter REDROOSTER as a profile name.
Create a profile, at the Name Your Rider screen, enter the following as names to unlock the corresponding cheats. Entered correctly the name of the cheat will appear onscreen.
All Riders - BUBBA
To unlock, All Tracks - ROADKILL
To unlock, All Vehicles - GENERALLEE
Successfully complete the ATV Academy Training and Trick Training to unlock the Dimension and Viper ATVs. Win over eight races in arcade mode to unlock the ATC ATV.
To unlock, Get Challenges - DOUBLEBARREL
Enter FIDDLERSELBOW as a Profile name.
Enter GINGHAM as a profile name.
When you enter your profile name, enter "GOLDRUSH" it will say everything has been unlocked. Then you can enter your name again (the one you desire) and still have everything unlocked.