Re: Core 2 Duo the best processor? What about Vista?
If you have to reactivate, all you have to do is call in and tell them the truth. You are allowed to upgrade your computer parts, it would be crazy for them to try to keep you from doing that. Just call and tell them you upgraded your processor and need to reactivate. They will give you the code to enter over the phone and you will be ok.
I once tried to install a legal but pre-activated version of XP in a virtual machine being hosted in Linux. The virtual machine shows all virtual hardware, not your actual hardware, so of course I had to call in. The guy questioned me about it, I truthfully told him I was only running this copy on one computer, and he gave me the code.
About the 64-bit thing, before going that route you should make sure there are compatible drivers and that your software will work with 64-bit.