Enter the following as your Profile name:

BUBBA - All riders
GENERALLEE - All ATVs
REDROOSTER - Champs
DOUBLEBARREL - All challenges
ROADKILL - All tracks
FIDDLERSELBOW - All tricks
GINGHAM - Max Stats

Beat the Academy Training and Trick Training to unlock the Dimension and Viper ATVs. Win more than eight races in Arcade mode to unlock the ATC ATV.