Do you have any of these programs installed?
- Apple Software Update
- Apple Mobile Device Support
- Apple Application Support
I had the trouble that if an old #4 or #5 was installed, a full iTunes install did not work.
If you have any of the above installed, try this,
Removing and reinstalling iTunes, QuickTime, and other software components for Windows Vista or Windows 7
So you likely have another program blocking the scripted Apple installer.
You might try a manual install.
The instructions below I've done with Windows 7 64 bit.
After downloading the latest version of iTunes from Apple, extract the files in “iTunes64Setup.exe”
(If you have never done this, you may need to download a program such as WinRAR [64 bit].)
Manually run each install file in the following order.
If there are any errors, stop, and write back with the results.