Please excuse Famine, when he's not goofing off he is relativly helpful (more than me) Any ways all games are encrypted in Hexadecimal, Hex for short. All GameShark, Action Replay, Code Breaker (and the newest cheating edition) CodeMajic do is just alter these codes. So lets say 4b5a7700 8ccd4321 is the health code (most of the codes like that are multi-line, but im 32-bittin') GameShark can chance the code to 4b4a7700 8ccd4444, and that might give you infinite health.
'nuff?