Pressing " D " and then " N " activates cheat mode. 
 Then enter any of the following codes:
 
 Code        Result 
 CORNHOLIO - Turns God mode on or off and gives you 
             unlimited jetpack fuel
 KROZ      - Turns God mode on or off and gives you 
             unlimited jetpack fuel
 COSMO     - Gives you unlimited jetpack fuel
 STUFF     - Gives you all the weapons, keys and full ammo
 ITEMS     - Gives you all of the items and keycards
 CASHMAN   - Makes you spew money
 VIEW      - Gives you a third-person view of Duke
 RATE      - Displays current frame rate
 SKILL#    - Changes the skill level
 HYPER     - Get high on steroids
 
 Type "D","N", then WEAPONS. This is similar to STUFF,