via Apple

Umh, be careful if you are using iTunes and you want to migrate to Vista…

[…] 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. […]

If you are upgrading from Windows XP or 2000 to Windows Vista prior to the next release of iTunes, here are a few steps that will improve your experience when syncing your iPod or playing iTunes Store purchases once upgraded to Windows Vista.

1. Deauthorize all iTunes Store accounts.
2. Enable Disk Use on all iPod models.
3. Uninstall iTunes.
4. Perform a clean install of Windows Vista (Highly recommended but not required).
5. Reinstall the latest version of iTunes.
6. Open iTunes.
7. Choose Authorize Computer from the Store menu in iTunes.