Hacking a save game file?

Its not actually hacking, its more curious fun :D

Anyway ive been playing Final Fantasy VII lately on my PC and suddenly gathered an interest to modify the save file through code. The structure of the save file is quite advanced to say the least. It comprises of:

The 3 Active characters
Items
Materia
Limit Breaks
Chocobo

and a few more i may of forgot. My question is, as the saved game file is encrypted into blah blah, would how can i decrypt the code to change various values around?

Any idea or tutorials around for such a thing, even if its a different game to learn the concept? :confused:

Cheers :thumb: