... who says open source doesn't mean wicked games!
Personally I'm a huge guitar hero fan... well acutally my whole house has gotten very into it (I have a Wii in the front room!). Anyway.. want that open source alternative, and not just a s**te one, try Frets on Fire. Frets on Fire is a game of musical skill and fast fingers. It is an open-source clone of the wildly-popular Guitar Hero game. It supports importing Guitar Hero I and Guitar Hero II songs as well as hundreds of songs composed by the community.
Oh it works on windows aswell as linux.
fretsonfire.sourceforge.net
Here is a video to take a look at (from the older version, the newer versions have better graphics, but its all about the gameplay):
http://www.youtube.com/watch?v=c5i6SxSAY4Q&feature=related