LEVEL SELECT:
At the title screen press 
S,S,S,S,S,T,T,T,T,T,T,T,O,O,O.

INVINCIBILITY:
Pause the game and press T,T,X,X,O,S,O,S,D,L. You 
should hear a sound, input the code again will turn
it off.

MAXIMUM POWER:
Pause the game and press U,U,D,D,L,R,L,R,X,O. You 
should hear a sound, you can also repeat this code
at any time during the game.