Let's try a complete uninstall and reinstall of itunes.
Go to the control panel and uninstall itunes, quicktime, apple software update, apple mobile device support, apple application support and bonjour. Then restart the computer and install itunes from
If that does not work,
In windows vista, click on your start menu, go to accessories, right click on the command prompt icon and choose "run as administrator". Once it opens, type in the following command...
netsh winsock reset
Now try to open itunes.
let me know whether this helps