Give Goldwave a try.
Removing vocals (not going into copyright here!) can be done fairly easily if the original recording was made in stereo and the vocalist was "centered" and the rest of the group was "off center axis" at least somewhat. If you have a "mono" file, give up before you even attempt this.
First of all get Goldwave from
http://www.goldwave.com
It is shareware but it will allow you to do what need with in the limitations of the shareware. (Buy it if you can afford it around $50. US and it's worth it!)
There is a "one button" remove vocal feature with various settings. It's works by performing a basic a phase cancel. Some settings work better than others, you can preview them all.
Be aware that, as some people stated here, you can rarely remove all of the vocal tracks but you can usually make it usable for live performances, etc. One of the big issues with completely removing thevocal is that the "reverb" applied, post production, to a track is usually "off axis". This means that it won't phase cancel.... so what you may actually be hearing (after the removal) is not the vocal track but the "left over" reverb...
One of the things that I do, that really works well for me, is to run both a "high pass filter" set at a frequency over 11,000 Hz and save whatever is left to a file. Then I run a "low pass" filter and save what is left to another file. Then I run the "vocal remover" and save that to a file. Finally, I merge them all back together and save them to a new file.
By doing this you are able to maintain (add back) some of the lows and the high frequencies that might have been removed from the vocal elimination. Again, you will have to adjust the high pass and low pass according the frequency range of the singer, so there is no simple solution.
Regards,
Joseph Pisano
http://www.mustech.net