It might be worth starting again, by uninstalling iTunes and related programs and then installing Quicktime separately form iTunes.
I will give a method below. It includes instructions for using the Microsoft Installer clean up utility, but you only need that if one of the uninstalls fails. If all the uninstalls go through without error, you don't need it.
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I would make copies of iTunes Library.itl and iTunes Music Library.xml (in the iTunes folder) before you start. I always like to backup my library databases before upgrading, just in case there is a problem.
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Download a fresh copy of iTunes and the stand alone version of Quicktime (the one without iTunes)- save them on your desktop.
http://www.apple.com/quicktime/download/win.html
http://www.apple.com/itunes/download/
Download and install Microsoft Installer cleanup utility, there are instructions on the page as well as the download. Note that what you download is the installer not the program – you have to run it to install the program. The installer doesn't give any message to confirm the installation.
http://support.microsoft.com/kb/290301/
(To run the program – All Programs>>Windows Install)
Now use the following method to remove iTunes and its components:
XP
http://support.apple.com/kb/HT1925
Vista
http://support.apple.com/kb/HT1923
*If you hit a problem with one of the uninstalls don't worry*, carry on with the deleting of files and folders as directed in the method.
When you get to deleting Quicktime files in the system32 folder as advised in the method, you can delete any file or folder with Quicktime in the name.
Restart your PC.
Run the Microsoft Installer Cleanup Utility. (Start > All Programs > Windows Install Clean Up)
Remove any references you find to the programs where the uninstall failed.
If you don’t see an entry for one of the programs that did
not uninstall, look out for blank entries or numeric entries that look like version numbers e.g. 7.x for Quicktime or 1.x for Bonjour.
restart your PC
Install the stand alone Quicktime and check that it works.
If it does, install iTunes.
