Cheat mode
 
 At the main menu, press Circle, Left, Right, Circle, Up, R2. A "Cheat"
 selection will appear on the options screen, allowing God mode, all
 weapons, infinite ammunition, infinite oxygen, no chestbursting, and
 level selection. -From: kissace69@hotmail.com
 
 Research mode
 
 At the main menu, press Square, Up, Down, Circle, Left, R1. A
 "Research Mode" selection will appear on the options screen. This
 mode allows you to change some of the game's Aliens and Facehuggers
 (shrinking them, making them wire-framed, semi-transparent, etc.).
 This is done by highlighting various sequences of grid squares.
 -From: kissace69@hotmail.com 
 
 Game Shark Codez:
 
 
 Max Reverse Joker Command
 D00BDB92 ????
 
 Infinite Health
 8010D620 2400
 
 Infinite Chestburst Time
 8005162C 0000
 
 Infinite Pistol Ammo
 8011BCC4 0064
 
 Infinite Shotgun Rounds
 3011BCD6 00FF
 
 Infinite Shotgun Ammo
 8011BCC6 0064
 
 Infinite Pulse Rifle Rounds
 3011BCD8 00FF
 
 Infinite Pulse Rifle Ammo
 8011BCC8 0064
 
 Infinite Flamethrower Rounds
 3011BCDA 00FF
 
 Infinite Flamethrower Ammo
 8011BCCA 0064
 
 Infinite Electric Gun Rounds
 3011BCDC 00FF
 
 Infinite Electric Gun Ammo
 8011BCCC 0064
 
 Infinite Grenade Launcher Rounds 
 3011BCDE 00FF
 
 Infinite Grenade Launcher Ammo
 8011BCCE 0064
 
 Infinite Laser Rounds
 3011BCE0 00FF
 
 Infinite Laser Ammo
 8011BCD0 0064
 
 Infinite Rocket Launcher Rounds
 3011BCE2 00FF
 
 Infinite Rocket Launcher Ammo
 8011BCD2 0064
 
 Infinite Small Medipacks
 8011BCE4 0009
 
 Infinite Medium Medipacks
 8011BCE6 0009
 
 Infinite Large Medipacks
 8011BCE8 0009
 
 Infinite Flashlight
 8011BCFC 00FF
 
 Infinite Portable Autodoc
 3011BD02 00FF
 
 All Weapons
 3011BCBC 00FF
 
 Items Never Decrease
 800525AE 0000
 
 Stop Timer
 8005C356 0000
 
 Press Select For More Time
 D00BDB92 FFFE
 8011BE0C 7080