Unlock any cheat and "Cheat Mode' will appear at the options screen.
Invulnerability:
Get all gold medals in Grand Prix Championship to unlock Invulnerability at the cheat menu.
Runaway:
Get all gold medals in Crash mode to unlock Runaway at the cheat menu.
Drivers Ed car:
Get all gold medals in Driving 101.
1997 Eclipse and 2001 Focus SVT:
Beat Custom Championship twice.
Two player Pursuit mode:
Beat Pursuit 3.