During the game choose the computer then type [G] and [0] (this is a zero) together, then enter any of following codes:

God mode                     5332
Quick computer scanning      9123
More damage to oppoents      2354
More health                  8216
All weapons                  2352
100% accuracy                4616
First-aid kits double effect 6235
Unlimited ammunition         2695
Cannot be heard              4982
Cannot be seen               8892
Full health                  4003
Always silent                0038
All other things             4828