What you're asking for jdreamer is a minus one track, no vocals but the guitar, bass, drum and <insert instrument here> remain the same.

And like everyone has posted, its very hard to just remove the vocals from the track.

Some sound cards can actually "soften" the vocals for you, like Abit's onboard sound cards ..... the driver allows an option to "remove" the vocals from the track your playing via Winamp or so. But you can still hear the vocals on the background, very softly.