TheGameSite: Tips, Cheats, Walkthroughs: N64: Aeorogauge
ENABLE ALL HIDDEN CARS AND TRACKS
Turn on the game and press Start on Controller One until you see the screen that says "Push Start" (if you see "Grand Prix Mode," you've gone too far). On Controller Two, press Up on the Control Pad, Down C, R Button, L Button, and the Z Button all at the same time. Release them, then immediately press Start or the A Button on Controller One to enter Grand Prix mode. All tracks and cars are now available.
