Type those codes in during the game:

 BRUCE             Invulenerability
 MURDERER          All Weapons
 NICK              Max out health
 SON OF SAM        Items
 DUSTIN            Warp to level 1
 BOSTON STRANGLER  Warp to level 2
 HELTER SKELTER    Warp to level 3
 CHARLES MANSON    Warp to end of level 3