At the name selection screen, enter (one of the cheats below):

 Code              Effect             
BIG CHEAT          All cars and tracks selection screen, enter  
LEAGUE CHEAT       All cars in Demolition Mode

Thanks to Revolution reader Fedrico Ferrari 84!

Codes

DWANZIL - More End of Race Points

Semi-Pro League Unlockables

Chicken (Game Mode) - Complete Semi-Pro League
Hunter's Quarry (Track) - Complete Semi-Pro League
Meltdown (Track) - Complete Semi-Pro League
Pelton Stadium (Track) - Complete Semi-Pro League
Predator (Car) - Complete Semi-Pro League
Pro League (Game Mode) - Complete Semi-Pro League
Scrap Heap - Complete Semi-Pro League

Rookie League Unlockables

Chase (Game Mode) - Complete Rookie League
Lyon Staium (Track) - Complete Rookie League
Mantis (Car) - Complete Rookie League
Renegade (Car) - Complete Rookie League
Semi-Pro League (Game Mode) - Complete Rookie League

Pro League Unlockables

Chemical Plant (Track) - Complete Pro League
Go Cart Carnage (Track) - Complete Pro League
Redneck Raceway (Track) - Complete Pro League

Endurance League Unlockables

All Reverse Tracks - Complete Endurance League
Vandal (Car) - Complete Endurance League

Arena League Unlockables

Suicide (Game Mode) - Complete Arena League
Widowmaker (Car) - Complete Arena League