All tracks:
Use the following steps to enable all tracks, including the alternate 
tracks. 
Set master difficulty and five laps per race at the options screen 
Press X on Li'l Dave at the 1 player select screen, then go back to 
title screen.
Press Up, Down, Left, Right, R2, R1, L2, L1 within four seconds at the 
title screen.
Set three laps per race at the options screen.
Press X on Wild Ride at the 1 player select screen, then go back to 
title screen.
Press Up, Left, Down, Right, Square, R2, Circle, L2 within four seconds 
at the title screen.
Set amateur difficulty and turbos off at the options screen.
Press X on Bomber at the 1 player select screen, then go back to title 
screen.
Press Up, Down, Left, Right, Up, Down, Left, Right within four seconds 
at the title screen.
Set professional difficulty and turbos on at the options screen. 
Press R2, R1, L1, L2, R2, R1, L1, L2 within four seconds at the title 
screen. 

Race as Enigma:
Set master difficulty and 6 laps per race at the options screen. Press 
Left, Square, Down, Triangle, Right, Circle, L1, R1 within four seconds 
at the title screen.