Start the game. Load a Tour Profile. Select a Level. Select "Start Game". 
After the "Loading" screen disappears, you will see a "flyby" of the level
layout. While this flyby is happening, type the word(s) of the Code(s) you
want to use and realize that there is no need to hit the ENTER key at the 
end either. When the level starts, your codes will take effect. The cheat 
effects only last during the current level. If you quit the level or complete
it, the codes are disable unless you re-enter them at the next level. 

Code    Result 
--------------
HOPHI  - Unlimited Mega Ollie Power-Ups 
SLOMO  - Unlimited Slo-Mo 
DIZZY  - DOuble Speed Spins 
GETALL - Activate ALL Cheats