I had the same frustrating problem. iTunes worked fine on my Vista 32-bit. I ugraded to Windows 7 64-bit and after installing iTunes it froze on start-up. I tried uninstalling and reinstalling it, used a registry cleaner, deleted old iTunes libraries, read forums up, down and sideways.
Finally, I found an old version Link Removed - Invalid URL and installed it. It ran, but the iTunes store wouldn't load. I updated that version through 'check for updates' and now it's running fine. Not saying it'll work for you, but it worked for me.
Cheers