Apple have a recommended order for uninstalling the components, and there are some other tips below...
Go to Control Panel > Add or Remove Programs (Win XP) or Programs and Features (later)
Remove all of these items in the following order:
- Apple Software Update
- Apple Mobile Device Support (if this won't uninstall move on to the next item)
- Apple Application Support
Reboot, download iTunes, then reinstall, either using an account with administrative rights, or right-clicking the downloaded installer and selecting Run as Administrator.
The uninstall and reinstall process will preserve your iTunes library and settings, but ideally you would back up the library and your other important personal documents and data on a regular basis. See this user tip for a suggested technique.
Some users may need to follow all the steps in whichever of the following support documents applies to their system. These include some additional manual file and folder deletions not mentioned above.
If you are running WindowsXP Pro there is one extra checkbox you must uncheck - when right-clicking the executable and selecting admin-level user, you may see 2 options: yourself and a generic ADMINISTRATOR field which requires a password you will not have.
Under XP Pro you will see a checkbox with a checkmark saying "protect my computer and data from unauthorized program activity"
After uninstalling from Add/Remove, and even deleting from C:Program Files, and after running the MS Fix It utility 3 times, I finally unchecked that box.
Downloads>ItunesSetup (right-)click>Run As... uncheck box "protect my computer and data from unauthorized program activity"
ALSO: earlier Setups install earlier version, which cannot find .itl libraries. Use today's installation executable to fix newer .itl headaches. Uninstalling from Add/Remove is not needed (under XP Pro). Installing most recent install executable will install over the top of previous releases.
I have been banging my head against this install FUBAR for 5 days now, and XP Pro has its own secret checkbox you must not miss!