Go back to the Options screen by press Left, X. Now set Difficulty to Professional and Trophy Presenter to "Rider's Choice". Return once again to the Main Screen and press Up, Left, Down, Right, Up, Left, Down, Right. If you did it right, you should hear a "Ka-ching!"
Enable Codes
Go to the options screen and set the difficulty to Professional and the number of laps to 6. Then go to the Main Menu and press Circle, Circle, Circle, Square, Triangle, Triangle, Square, Triangle. You'll hear a "Ka-Ching!" and "Codes Enabled" will appear on the screen.
Air Brakes
R1, R2, Right, L2, Up, Circle, Up, Circle
Double Stunt Points
Right, Up, Circle, L2, Triangle, Circle, R1, R2
Ice Racing
Up, R2, R1, Right, L1, Square, Right, Right
Rocket Racer
Triangle, Up, Up, L2, L2, Up, Up, Up
Show-off Camras
Triangle, Down, Square, Triangle, L1, L1, R1, R1
Super Agility
Down, Circle, Left, L1, Left, Right, Left, Right
Two Player mode with other Bikers
Circle, Square, R2, Circle, Triangle, L2, Right, Up
Unlimited Turbos
Triangle, Circle, Right, R2, Up, Square, Up, Triangle
Zero Resistance
Square, L1, Triangle, Right, L1, Down, R2, Triangle