Just type in 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).