Wel I have found a really cool version of Guitar Hero that you play on your keyboard that is open source so absolutely free!
You can also download songs to put into it - people have put quite a few on the internet - including songs from the real Guitar Hero!
It's called Frets On Fire
to get songs go to the following website and then create a free user (you cannot find the links otherwise, which are from rapidshare and similar)
then when you have created a user go to the section on the forum called tunes posting
and then you can go from there!
Have fun! I really like it
Also, it apparently works if you plug in an ordinary Guitar Hero guitar too! http://www.joystiq.com/2007/04.....s-on-fire/