Various Cheats:

During play press F10 then enter one of the following codes

GIBNPLENTY Dismemberment
T2000 Skin Like Terminator
GIVEMEFAITH Max Health
IWORKFORGOD Invincibility
GETINTOMYBELLY Get All Weapons
BIGHEAD Get Big Head Mode
NOD3D Invisibility
HELLFREEZEOVER Freeze Enemies
BIGSTICKOFDEATH Get Shotgun
MEDIUMRARE Get Crossbow
GOODTIMESMAN Get Dynamite
BURNYOURASSOFF Get Flamethrower
MEETMYPALTOMMY Get Tommygun
SMILEYNOMORE Get Elephant Gun
SUNOFGOD Get Charge Radiance Emitter
IAMAWIMPFORTHIS Get 100 Bullets
RECHARGE Restore Flashlight Battery
THEDOGFARTED Get Gas Mask
ICANSEE Get Night Vision Goggles
WWBEWARE Get Silver Bullets
VAMPBEWARE Get Lith Bullets
DEMONBEWARE Get Mercy Bullets
ISUCK Get Easy Difficulty
IRULE Get Hard Difficulty
COMBATISSCARY Easy Combat
PUZZLESARESCARY Easy Puzzles
INSTANTCRASH Crash The Game
THUNDERSTORM Make Storm
SNOWSTORM Make Snow
FLAMEONASTICK Ammo is Flaming
ITISDARKNOW ????
GONEAWHILE ????
RAISE ????
NUKEFART ????
TIME ????
OLDHAT ????
BLANK ????
DARK ????
STEP ????