Go to the "Options" screen, then select the "Cheat Codes" option and enter one of the following codes:
All paint jobs: R4MONE
All tracks: MATTL66
All tracks and mini games: IF900HP
Bonus mini game: TRGTEXC
Unlimited boost: VROOOOM
Fast start: IMSPEED
Concept art: CONC3PT
Movie clips: WATCHIT
All cars: YAYCARS