Whether the file is an mp3 or a wav it doesnt matter.
The problem is that the music is already rendered as one track and it is quite hard to do.
You may be able to play around with some settings in Audacity and cut out some of the frequencies to take the vocal out.
You will find however that you will loose parts of the track and quality when doing this.
There is probably a way of doing it in Ableton but it would take a while and again you will loose some of the tracks sounds and quality whilst doing this.
Maybe there is some software out there that is more dedicated to getting it done quicker but I'm not aware of any that will do a good job without causing the track to suffer as well.
There are a few tutorials on youtube but like I said it isnt easy to get it sounding perfect.
http://www.youtube.com/results?searc...ve+vocals&aq=f