Where can I d/l a <b>FREE</b> *.IDF MIDI Instrument Set file off of the 'net? Preferably and XG, but I'll settle for GM if an XG is nowhere to be found.
P.S.: *cluelessly* What does XG stand for, anyway?
You can get a description of idf files at:
http://www.pgmusic.com/techfaq.htm#2-9
As mentioned in the article, microsoft has an idf editor that might be of use to you if you're interested.
XG is Yamaha's proprietary extension to General Midi. It includes GM, but also includes a substantial number of refinements. Needless to say, if you want to make the most out of XG files, you need a Yamaha synth.
Roland has a similar GM extension called GS.
For more information, go straight to the source, at:
http://www.yamaha.co.uk/xg/