Guitar Hero III is scheduled to be released in October on the consoles and PC. Aspyr will release a hybrid Windows/Mac box, complete with USB guitar. System requirements haven't been released yet, but I'd expect any PC version to have everything the console versions do. The complete setlist contains pretty much any kind of rock you're interested in, from Rage to Bloc Party to Kiss, and even the D and gamer favorite DragonForce.
Sounds awesome. Considering the guitar is just a USB device, how cool would it be to integrate it with Garageband? Here's hoping Aspyr stays on beat, and makes the PC/Mac version available shortly after the console release. Until then, you may always rock it out with Frets on Fire. Throw the horns!