Thanx all.
Dana, I stumbled upon that Garageband/iTunes option just last night while searching Youtube ( 'WAV to MP3 conversion' ). I'll give it a try today. Be interesting to see what size file I end up with for a 3 - 4 minute song with 4 tracks of instrumentation within the Garageband file ( drum beat, rhythm guitar,occasional lead guitar and a little slide/simulated pedal steel sound ).The next song I do will have a vocals track also.

If I can get them down to Outlook email friendly size ( MP3 quality isn't the priority as it's only a backing track for home practice use )then I'm up, up and away.