Enter "ASHRUBBERY" as a driver name to unlock all paint jobs.
At the enter your name screen, enter ILUMBERJACK as your name.
Enter "DEADPARROT" as a driver name to unlock all tracks.
Enter "CRUNCHYFROG" as a driver name.
To enter the cheat simply start a new race and enter your name as ILUMBERJACK. You'll now hae all of the cars unlocked.