Start game, goto console (hit tilde ~) and enter the 
following cheats: 

Cheat       Result 
------------------
god       - Toggle God Mode 
ExitLevel - Level Skip 
noclip    - Toggle Spectator Mode 
kfa       - Get All Weapons And Full Ammo 
heal      - Heal 
FragSelf  - Guess What.. 
morph     - Cuts health, get Excalibur 
            (If this code is enabled too many times, it will end your game)