This is a hobby I take interest in, but some of you might not know much about it.
Romhacking is the modification of ROMs (Read Only Memory) or any other game files. It can include modification of music, graphics, text, programming, etc.
I myself have been working on translations, or modifying the game so that it's in a different language (for me Jap --> Eng). I don't do the actual translation, just the hacking part.
####I'll include more, I'm kinda in a hurry####
Some interesting links:
http://www.romhacking.netPretty much the definitive place for romhacking info. I also frequent there.