CheatCodes:

Enter one of the following during game:

IDDQD -- God mode. 
IDKFA -- full ammo, 200% armor, all weapons. 
IDSPISPOPD -- You can walk through walls. 
IDBEHOLD -- Displays menu (Followed by S, V, I, R, A or L). 
IDCLEVxy -- Warp to episode x (1-3), level y (1-9). 
IDMYPOS -- Shows your coordinates in hex. 
IDCHOPPERS -- Gives you shainsaw. 
IDDT -- Changes the map view between normal, full and full with objects.