Invasion From Beyond Cheats

Level select:
In the PRESS START screen, push L1, R1, L2, R2, Triangle, X, Circle, Square(2), Circle, X, Triangle . Go back to the START MISSION screen to pick any level in the game.

All ships, weapons, and upgrades:
In the PRESS START screen, push L1, R1, L2, R2, Up, Down, Right, Left(2), Right, Down, Up .