Yeah, I'd be shocked if MS hadn't done something to prevent you from doing that. I think part of their registration process includes looking at hardware serial numbers or somesuch. Not sure what they do, cause they DO need to support people upgrading their hardware.

This is an interesting question: They want to ensure that you can only install it on one computer, but how much upgrading/changing is needed for that computer to be considered "not the same computer"? I mean, I could replace a fried motherboard and a broken hard drive, and I'd expect it to still work when I re-install on the replacement parts...

Assuming it does manage to run, I'd say it would crawl pretty horribly.