Juiced Cheats
Head for the in-game cheats menu to unlock the following effects:
FAST - Unlocks infinite money (Career Mode)
PING - Unlocks all cars (Arcade Mode). If that hasn’t worked then try putting in PINT instead and hopefully that will unlock all the cars in arcade mode (courtesy leosdemise).
Juiced Unlock: All Prototype Parts
Finish the game with 100% respect from all computer players. You must have 1,500 respect points from all of them to accomplish this.