Download and install Cheat Engine... download the CT file for the game (I ended up updating the addresses on the one that was posted, and posting it to the thread on the game). Run the game, then open the process list with CE, pick the game, check the checkboxes you want while playing.
I'd advise not using infinite health or mega damage... both of them apply to enemies too, sometimes. Infinite mana and unlimited items will do you just fine. Unlimited bombs, especially, make short work of enemies.