When uninstalling, did you also download and install the Windows Installer Cleanup Utility, delete the leftover files in system32, and remove all leftover Quicktime components?
If you missed one of the above steps, do this:
1. Follow all steps located here:
http://docs.info.apple.com/article.html?artnum=93698 (be sure to grab all leftover files in Program Files and system32).
2. Download and install the Windows Installer Cleanup Utility (
http://support.microsoft.com/kb/290301).
3. Opens the utility, remove anything for Apple, iPod, iTunes, or Quicktime.
4. Re-download and install iTunes from
http://www.apple.com/itunes/download
If the same error appears after that, do steps 1-3 again, but then go to Start>Search, choose to search for 'All Files and Folders', and search for Quicktime. Delete everything that comes up (except if you see any Java files, as those don't delete properly). Also, if you come across any files that don't say 'Delete', skip them, and if you get an error when deleting a file, skip it as well. Try reinstalling again.