At the code entry screen, press Square(3), Circle(3), Triangle(2). Note: In the PAL version of the game, press Circle(3), Square(3), Triangle(2) at the code entry screen.
At the code entry screen, press Square(2), X, Triangle, X, Circle, X, Circle.
At the code entry screen, press X, Triangle(3), X, Circle, X, Square.
At the code entry screen, press X(3), Triangle, Circle(2), Square, X.
At the code entry screen, press Circle(2), Triangle, Square, X, Triangle(2), Square.
At the code entry screen, press Triangle(4), Square, X, Circle, Square.
At the code entry screen, press Square(2), Triangle, Circle(2), X, Square, Triangle.
At the code entry screen, press Triangle, Square, Triangle, X, Triangle(4).
At the code entry screen, press Triangle(2), Square, X, Circle, Triangle, Square, Circle.
At the code entry screen, press Square, Triangle, Square, Triangle, Circle, X, Circle, X.
At the code entry screen, press X, Triangle, Square, Circle, Triangle, X, Square, Triangle.
At the code entry screen, press Circle(3), Square(3), Triangle, Square. Alternately, successfully complete the game to unlock the classic Centipede game at the "Atari Games" menu. Note: If it is not unlocked as soon as you complete the game, restart your PlayStation 2, reload your game, and recheck the "Atari Games" menu.
At the code entry screen, press Circle(3), Square(3), X(2). Alternately, in the vet's office on level 13, walk into the small office on the far right side. Approach the computer and press X to play the classic Missile Command game. Then, successfully complete the level to unlock the game at the "Atari Games" menu.
At the code entry screen, press Triangle, Circle, Square, X(3), Triangle, Circle.
At the code entry screen, press X, Square, X, Square, Circle, Triangle, Circle, Triangle.
At the code entry screen, press Circle(3), Square(3), Triangle, X.
This Boss battle will be your mission in level 5. Press the buttons as instructed by the bottom captions. Do this at random so that the Infiltrator cannot predict your attack. When his health is down by 24, he will get a limp leg which will slow him down.