NationStates Jolt Archive

I've got a question for ya'll. My sister has Guitar Hero 2 (PS2), and I'm thinking about getting Guitar Hero 3 (XBOX 360). I've seen youtube videos of songs that people have added to the game. Now I'm asking, HOW DO THEY DO IT? Please, give me advice. Thanks.

They rip the game off a DVD/download a ROM, hack it, insert new songs and burn it to a new disc. I have no idea how, and I'm pretty sure it's illegal.

If you look, there's some videos on YouTube explaining how.