Hardcore realism mode
Press Up, Down, Left, Right, White, Up, Down at the main menu. Alternately, get a 100 point rating on a track to unlock the hardcore realism mode option for that track.

Shoot paintballs
Select single race or head-to-head mode. Press Up, Down, Left, Right, White, Up(2) at the "Race Day" screen. Use your horn (press Up) to shoot a paintball. Note: This also works in two player mode. Alternately, select practice mode and press Up, Down, Left, Right, White, Down(2) to enable paintballs.

View credits
Press Up, Down, Left, Right, White, Left(2) at the main menu.

High suspension
Press Up, Down, Left, Right, White, Left, Right at the main menu.

Mini cars
Press Up, Down, Left, Right, White, Down, Up at the main menu.

Wire frame cars
Press Up, Down, Left, Right, White, Right, Left at the main menu.

Richard Petty
Successfully complete all Heat challenges with a bronze or higher rating.

Computer Controlled Human Player
First enter the cheat for paintball then go to multiplayer & with at least 2 people. Let one person get heavily damaged: let them go into pits but don't follow in stead enter the pits at an angle so as not to be controlled by the pit computer; now shoot the other player out onto the track before there pit stop is over. Now they are under the computers control and will race the rest of the race.