Apparently iTunes, iPods, and Vista don’t play nice just yet. A variety of issues have been reported, including: purchased tracks not playing, synchronization glitches, and computer gremlins “may corrupt your iPod.” Apple warns:
iTunes 7.0.2 may work with Windows Vista on many typical PCs. Apple recommends, however, that customers wait to upgrade Windows until after the next release of iTunes which will be available in the next few weeks. Apple is preparing to address a number of iTunes compatibility issues in the next release of the software.
Apple suggests folks who have upgraded to Vista reinstall the current (buggy) version of iTunes and to use their repair tool to authorize playback.