You can take away the vocal, but not without destroying the music. But just for kicks, invert both the left and right channels, which will (essentially) eliminate anything panned right up the middle, which vocals often are.
I think Chrisjob meant invert the left OR right channel. If you invert BOTH of the channels you won't get the phase cancellation that you are looking for. The problem with this method of attempting to remove vocals is that you will also greatly reduce the level of any instruments that are panned to the center. For most material it is highly unlikely that you will eliminate the vocal but you may reduce the level sufficiently for your needs.
seriously though..
you will get a poor quality product most if not all of the time..even if the vocals are right up the middle the effects on them that widen the spectrum a bit will stay behind and leave a mess of things...
Dunno about you guys but, I just make my own 'minus one' tracks by using a midi sequencer program then record it into Audition, then add backing vocals. Aaah, the rewards of being a keyboard player.
You may also want to check out one of the auto arrangement programs such as Band in a Box or Jammer. There are others. Depending on what your hoping to use it for it could be a good alternative. With Band in a Box you just type in the chords and pick a style. The results are often quite good but the quality of the sounds depend on the MIDI device that you use. I bought Band in a Box a few months ago and have been very happy with it.