Various Cheats
     At the Zone Selection screen, pause gameplay and press any of the
following:

L1, R1, L1, R1    - Unlock 1st Level
L2, R2, L2, R2    - Unlock 2nd Level
L1 + R1 + L2 + R2 - Unlock 3rd Level, secret power-ups, and 
                    3 classic black and white Pong versions.