Press UP, DOWN, LEFT, RIGHT at the main menu. This will take you to a cheat screen where you can enter any of the following codes.
Police warning instead of ticket: Enter LETMEGO as a code. The first three times you are pulled over the cop will only give you a warning.
Police car: GOTPOPO
Mazda RX-8 in arcade mode: RENESIS
1996 Toyota Supra RZ: SICKJZA
1999 Mitsubishi Eclipse GS-T in arcade mode: IGOTGST
2004 Toyota Celica GT-S Action Package: MYTCGTS
Free car repair: FIXITUP
Pac-Man vinyl: GORETRO