Drive as a Tow Truck
GO TO RACE SETUP SCREEN AND CHOOSE CAR SELECT.SELECT BOBBY LABONTE OR KENNY WALACE THEN HOLD C AND PRESS UP, DOWN THIS DOESN'T WORK IN 2 PLAYER MODE.

Fat Car Mode
Go to game options screen and highlight stereo. hold Z and press B then X then Y and stimultaneously press A and B. you should hear "GO BUDDY GO GO" now start the race and press START+A+B+C. when the game reloads your car will be twice as big