Here are the DN3D cheat codes:


dnkroz - god mode on/off
dncornholio - same as dnkroz
dnstuff - all weapons, full ammo, etc.
dnitems - all inventory items, keycards, etc.
dnscotty## - warp to episode# level#
dncashman - duke throws a bunch of cash every time you use the "open" 
key or    
button
dnview - a change of perspective
dnrate - displays the framerate
dnskill# - change the skill level
dnhyper - ???
dnmonsters - ???
dncosmo - gives you message "register cosmo" or something like that
dnallen - another message, this time about Major Stryker


Those are the only cheat codes that I know so far.  If you find any 
more, please
send me a message.  BTW the cheat codes will not work if you have 
remapped the
"D" on your keyboard for something.