Populous 3 - The Beginning cheats and cheat codes for PC

Press TAB + F11 on your keyboard, then type "buyme" or "byrne" and hit 
ENTER at the window that appears to enable cheat mode. Then, press any 
of the following key combinations to avtivate the indicated cheat effect:

Code - Effect:
Tab + F1 - Instant Training mode
Tab + F2 - Free spells
Tab + F3 - All spells
Tab + F4 - All buildings
Tab + F5 - Refill mana

Choose bonus level:
While playing (at any level), press the F12-button and after that press the 
F11-button. Then you get a demo. If a level passes you want to play, press 
the spacebar or the enter button than you play the game from the moment you 
have chosen.

Play demo:
While playing the game, hit F11 and click a button during the rolling 
demo to play on it. 

Go to any planet:
After entered to the tutorial mode type "ptb6". Then, go to "New Game" 
and watch the ending sequence. You should now be able to see and go to 
all the planets in the solar system at any time.

Alternate cheat mode:
Hold O to display the cheat menu in the lower right part of the screen. 
Then press Cursor Up or Cursor Down to scroll through the menu, and 
press Cursor Left or Cursor Right keys to activate cheats.