Straight from Slashdot:
"In our office we've been running an older 5gb iPod with both Macs and PC's (using Xplay), but when we installed iTunes for the PC the iPod stopped working. Songs and playlists transfer over fine, and you can see them and play them in iTunes, but you can't listen to them on the iPod, itself. It shows the song details and so forth, but skips through the tracks, playing 0 seconds of each one until it finishes. This only applies to tracks added since iTunes was installed. No amount of reformatting, or rolling back firmware seems to work. When I called Apple, they stated that they simply don't support the use of the older Mac iPods on PC's and are not responsible, even though they admit that it was their own software that caused this."
News source: Slashdot