You're quite welcome and I'm delighted that you enjoy them :-)
I don't suppose you know of a freeware program that I can use to remove voice tracks from Mp3's? I've tried a karaoke program and could never get it to work.
I'm no expert on audio but I'll take a stab at your question; If I'm wrong at any point, I hope that others will jump in to correct me.
My understanding is that when you are dealing with an MP3 audio file, it has already been downmixed into two distinct audio channels, Left and Right stereo, and the individual instrument and vocal tracks no longer exist as distinct, editable identities as this point. Therefore, the concept of a 'vocal track' per se, does not exist in an MP3 file, only on the original master tape.
So, I believe that the only way to do this is via an equalizer, where you lower the gain of the audio frequencies that correspond to the vocal range in the given file. The problem with this of course is that you will also eliminate any instruments that occupy that same range as the vocals do. How objectionable this will be will depend upon the specific piece of music and your intended use for the end product. If the instrument range goes far beyond the vocal range then you may have 'something' left, but if the instrument range is similar to that of the vocal range then you may not have much at all left to work with.
I did a web search for 'freeware audio equalizer" and got 726,000 hits, so it looks like there may be just a few to choose from if you want to give this a try :-)