CODES:
(Enter these codes at the main menu or in the options screen)
Access any section of a level: R1, Down, R1, Right, L1, Up, L2, Square
Cheat Mode: Press O, LEFT, RIGHT, O, UP, R2
Infinite ammo with weapons: L1, L2, Up, L1, L2, Up, Circle
Infinite health: R1, R2, Down, R1, R2, Left, Square
No chestbursting: R1, L1, Left, R1, L1, Square, Down
No drowning: R2, L2, Right, R2, L2, Circle, Down
Obtain the weapons you can have in that level: L1, Circle, Square, L1, Down, Up, Circle
Quitting the game instead restarts the level: R1, Triangle, Square, L1
Research Mode: Press square, up, down, circle, left, R1.
While playing the game, hold down L2 and press L1 for debug info: Triangle, L1, R1, Square, L1, R1, L1, Square

BOOT ANY GAME DISC:
To boot any other game to bypass region and disc checks, first open the CD tray and wedge something into the tray open sensor so you can see the disc spinning during play.
1) First activate the Cheat Menu and level select codes.
2) In Options, press Left, Up, Right, Down, Right, Up, Left, Square, Triangle, Square, Triangle, L1. A sound should be heard.
3) Enter the Cheat Menu and choose Level 6 (Military Systems Complex), Section 1.
4) Get your other game disc ready, then hold L1, press X to enter the level. Keep holding L1 and the game disc should stop spinning. Now swap the disc with another game, then hold Square and Triangle, then release all three at the same time. The new disc you inserted should now boot.