You might look into soundfonts. You can download a version of the RGC:audio SFZ player here: http://www.soundbrewer.com/pages.php?pageid=20. Since you'll be running it in BIAB it should work ok in Win7. I don't know for a fact but it should.

There should be a gm sound font called - 32MbGMStereo.sf2 - floating around the web and it sounds pretty decent. I can't seem to find a link at the moment but there's a couple of fairly good gm sound fonts out there if you can find them.

Several members on the forums here have some gm soundfonts and they might know of some links to them.

Later,
Jim