Press [PAUSE] then type:

Code - Result

cheatcheat - Enable Cheat Codes
ammo - Unlimited Ammo
godmode - God Mode
fly - Fly Mode
invis - Invisibility
winmission - Win Mission
losemission - Lose Mission
stats - Show Game Stats
ac919 - God Mode, Unlimited Ammo, Fly Mode
hitlermode - Enemies Don't Die