while playing, pause your game and press, C-U, C-D, C-L, C-R.  A cheat 
option will appear on screen.  Enter this menu, then quickly enter one of 
these codes:

God Mode:	C-L, C-R, C-D
Full Health:	C-L, C-U, C-D, C-D
Level Select:	C-L, C-L, C-R, C-R, C-D, C-U
Butcher:	C-D, C-U, C-L, C-L
No Clipping:	C-U + 20, C-D