Start a game with either Human's or Orc's,
Go to the password screen and enter these passwords to get the following:
TSGDDYTD - invincibility
THRCNBNL - finish the game
MKTS - faster productions
NSCRN - reveals map
VRYLTTL - upgrades magic and gives you all spells
DCKMT - upgrades everything to maximum possible
NVRWNNR - lets you continue playing even after you've achieved your goal
YPTFLWRM - makes you lose the game
VLDZ - gives you 5,000 oil

You must go back to the game after each one you enter is finished and it will enable the cheat.