Enter the following during play:
IFYOUTHINKYOUAREHARDENOUGH - All weapons and unlimited ammo COMEANDHAVEAGO - All weapons NADIAPOPOVXX - Level Warp (where XX is 01-34) TAKEONALLCOMERS - Infinite energy
In the password box, type G0LVL and the number of the level you want.
(e.g. G0LVL5 and you will go to Level 5).
Thanks to Revolution readers Jason Bennet, Christof Sperl, and Pavel Spirine!