This all has to do with the anti-piracy system M$ uses. When you install, it detects your hardware. You can make minor hardware changes, like a new hard drive, change of video card, add more RAM, simple things like that.

Change the motherboard and you're toast. That is considered a "new computer".

Why do you think I stuck with Win2K for so long? If I built a new computer I didn't have to worry about re-authenticating it.

But even without that you'd likely have problems just putting the drive in a new computer because the drivers are different for different hardware. Even Win2K has a small fit when I do that. I still have a drive with 2K on it as a maintenance/emergency system and it complains a little when I put it in a different computer than it was the last time.

I'd suggest deciding on a set of hardware and getting the OS installed, and leave that one system alone. Experiment with others, but you'll need a known good reliable setup that you can always resort to when things go wrong.

Brian