/\/\/\
Codebreaker works most similarly to Gameshark. No you do not need a modded-PS2.
Basically you load the cd (Codebreaker, Gameshark, and Action Replay), create/enter your codes (if they are not preloaded on the disc), enable the codes, then you go to start game. The UI will prompt you to insert the game disc (most will automatically open the disc drawer for you), change discs to the game disc, and play the code-modified game.
Basically what you are doing with a cheat device, is changing/locking memory values. So rather than the game reading the original data, the data read, has been modified by the codes to new values. This Memory manipulation allow you to do many really interesting things to your games, anywhere from simple money cheats, Time freeze, completion flags, power multipliers, infinite lives, all the way through the more complex, like GT4 Car Hybridization. Also you can attach button codes to the codes, so you can activated/deactivate codes while playing.
If you like making games do what they are not designed to do, then you will get a lot of fun out of a Codebreaker/GameShark/Action Replay. Although beware of Codebreaker, as it is no longer supported, and it is hard to find 'Day 1' code downloads. I basically only use my Codebreaker for save transfer, and an Old Gameshark for most of my game manipulation.
