Enter these at the main menu:
Granted Wish - Cheat Code
Unlock ACME Factory - L2, R1, R2, Triangle, Circle, Select
Unlock Planet X Speedway - R1, Square, Circle, L2, Triangle, Select
Unlock Wackyland - L1, Circle, Square, R2, Triangle, Select
Unlock Planet Y - Right, Left, Triangle, L2, L1, Select
Unlock Forest Speedway - Triangle, R2, Left, Triangle, L1, Select
Unlock Garden Speedway - R1, Right, Left, L1, Square, Select
Unlock Rocky - Triangle, Left, R2, Circle, Circle, Select
Unlock Pepe Le Pew - Left, Right, R1, Circle, Square, Select
Unlock Yosemite Sam - Left, Right, R2, Square, Circle, Select
Unlock Foghorn Leghorn - Right, Right, L2, Square, Square, Select
Unlock Sylvester - Left, Left, L1, Triangle, Circle, Select
Unlock Granny - Circle, Triangle, Triangle, L1, R1, Select
Unlock Duck Dodgers - L2, Square, Square, Triangle, Circle, Select
Unlock Gossamer - Triangle, Circle, R2, R1, Square, Select
Unlock Genie - Square, L1, R1, Triangle, Circle, Select
Unlock Hector - Triangle, L2, L1, Triangle, Square, Select
Unlock Evil Scientist - Square, Circle, L2, R2, Triangle, Select
Unlock Duck Dodgers Speedway - Circle, Left, Square, Square, R2, Select
