The folks over at the Scorehero forums are at it again, hacking their way through Guitar Hero II. This time, they've managed to replace songs found in the game with custom songs, new note charts and all. A huge list of custom songs (including tunes by Dragonforce, Metallica, Journey, and more) can be found in this thread.
While the original poster in the "How-To" thread claims the process is idiot-proof, I beg to differ. It requires eight separate freeware program downloads, involves a 12-step process that makes my head hurt just looking at it. You'll also need a PlayStation 2 modified to play "backups." Eye of newt, virgin's blood, and horn of unicorn are optional.