a long time ago i found this website with a lot of backtracking's of songs that you could d.l now if anyone knows of that site or any of that matter, please share with me!
erm.. may be a bit of a stretch, but you could use guitar pro tabs, and turn the volume off for the part you play...
Another is http://www.guitarbt.com/
This guy on Youtube makes a few.
thanks a bunch guys, and RCShadow that was the one i used a long time ago
there are also a few quite good quality ones here