For the full version:

 please god     = Invulnerability
 please refresh = Max out energy
 please fly     = Fly mode
 please ghost   = No clipping mode
 please tellall = All messages
 please giveall = All weapons
 please open    = Opens closed doors


 For the demo version:

 The same cheats as in Serious Sam work here despite the 'please giveall'
 cheat:

 please god     = Invulnerability
 please refresh = Max out energy
 please fly     = Fly mode
 please ghost   = No clipping mode
 please tellall = All messages