iTunes for Windows XP: Troubleshooting unexpected quits, freezes, or launch issues – This article provides some general suggestions when trying to troubleshoot an issue where iTunes for Windows won’t open or unexpectedly quits. It may be useful to print this document before following the steps outlined below.
Learn about troubleshooting iTunes for Windows in Windows Vista or Windows 7.
If you are having trouble installing iTunes, go here for help. However, if you see one of the following specific error messages, click on the corresponding link for more information.

The iTunes application could not be opened. An unknown error occurred (0×666D743F)
iTunes 7 for Windows: iTunes had detected an audio configuration problem

http://support.apple.com/kb/TS1421