Enter these cheats during gameplay:

nvagod       God mode
nvablood     All weapons
nvashowmap   Full map
nvaclip      Toggle clipping 
nvalevel###  Skip level, where ### is the episode and level 
             (ex. nvalevel104 - tour of duty 1, level 4)
nvadebug     Debug mode   
navlevel     Level select   
nvamatt      Radioman follows   
nvduke       Toggle radio   

Thanks to Revolution readers Daniel M., Dork, Jim Gottenberg, Sean Hummel, Zachary

Lloyd, Jonathan E., Bud and Wiser, Dan D., Dennis L Evans, Valentin Perelogin,

Xer0derm, CreatoR, Chris, Josh, and Jeremiah Stark!