MDK (cheat)

To use these codes, hit the F1 key to get to the help screen first.
Most of these codes can only be used once per level.

HEALME - full health
INEEDABIGGUN - super chain gun
HOLOKURTISFUN - dummy item
TORNADOAWAY -  tornado item
NASTYSHOTTHANKS - homing sniper grenade ammo
KILL - kill yourself
To use this code, just type it in after the drop from space on the first level:
SHOWMOVIEMDKBZK - play hidden movie