If I have the music track and a music+vocals track, is it possible to seperate the vocals?
If the music track is identical to the music in the vocal+music track, then you could invert the phase of the music track and mix it with the combined track, which (algebraically, at least) is the same as subtracting it from the v+m track.

You may find that some additional compression, level shifting or EQ was done to the v+m track, which would make the subtraction less than perfect.