Sega GT cheats, and Codes for DC.
Unlock W.S.K. (World Speed King) Races
Complete all Official races and Event races to unlock the first ending sequence and the W.S.K. Races. The WSK Races are Front Drive Car Cup, Rear Drive Car Cup and 4 Wheel Drive Car Cup.
Like some other Dreamcast games, you can perform an infinite money cheat using two memory cards/VMUs. Just buy a car, and save your game on both VMUs. You can then send the car from one VMU to the other, and sell them. You can do this over and over again.