Well, I think I found the answer to the problem. I hope it helps everyone who uses Macs to maintain their music collection in iTunes.
When copying files from the Mac to a USB drive, Mac OS X will include resource forks and other files.
Turn on View Hidden Files in Windows Explorer and duplicate files starting with . can be seen.
Blue Harvest, a utility from
http://www.zeroonetwenty.com/blueharvest/how-to.html, can delete these and other Mac OS X files from USB and other drives.
Very nice utility! Well worth the purchase price.