At the main menu, select "EA Sports Extras", then "Cheat Codes". Then, enter one of the following codes to activate the corresponding cheat function:

All cars in Chase mode
Enter "CHECKERED FLAG" as a code to unlock all cars in Chase mode.

All fantasy drivers
Enter "RACE THE PACK" as a code to unlock all fantasy drivers.

EA Sports car
Enter "EA SPORTS CAR" as a code to unlock the EA Sports car.

Wal-Mart track and car
Enter "WALMART EVERYDAY" as a code to unlock the Wal-Mart track and car.