Press F2+F3 at the Main Menu. CHEATS ON will flash on the screen.

Press + and BACKSPACE for the cheat prompt, then type in these codes:

TURBO = Turbo mode
SCOUSER = Enable playtester keys
PAPARAZZI = Screenshot mode on - press insert to make one, will save in C:TEMPPIX
ALLOW SINGLE = Single player on multi-level
EVERY LEVEL SAVE = Enable save after each level
THE WHOLE OF CREATION = All cheats off

Playtester keys:
F1 = Ammo cheat
F12 = Health cheat
Shift-F9 = Skip level