Press 'Enter' during game play then type in the 
following cheats...

debugkeys               Debug Keys On

When entering debugkeys, press F10 to enter debug 
mode.  These are the keys that work in debug mode.

F2                      - screenshot
F6                      - change view
F7 or F8                - instant death
F9                      - return to normal view
F10                     - toggle debug mode
F12                     - skip level
[ or }                  - adjust lighting
1 and 3 on keypads      - change screen resolution
A                       - toggle AI
V or B                  - rotates view