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A number of things can cause iTunes library instability. I would start by loading iTunes in Safe Mode to see if perhaps a 3rd party plug in is causing an issue.
iTunes: Troubleshooting issues with third-party iTunes plug-ins
If the issue persists then I might recommend uninstalling and re installing iTunes and its associated softwares.
Removing and Reinstalling iTunes, QuickTime, and other software components for Windows XP
And it might also be a good idea to recreate your iTunes library if none of that works.
iTunes: How to re-create your iTunes library and playlists