Codes
Type in the following codes during gameplay:

idbeholda-Full automap
idbeholdi-Temporary invisibility
idbeholdl-Light amplification visor
idbeholdr-Anti-radiation suit
idbeholds-Berserker strength
idbeholdv-Temporary invincibility
idchoppers-Chainsaw
idclev[episode number][map number]-Level select
iddqd-Invincibility
iddt-Toggle full map; full map and objects; normal map
idmus[level number]-Change music to indicated level
idmypos-Display coordinates and heading
idkfa-All weapons, keys, ammo, and 200% armor
idspispopd-Walk through walls