Just for clarification, here's the situation.

If you have Windows installed on one computer and want to install it on another with the same liscense (cd-key or cd) you have to uninstall it on the first. You are allowed to have only one installation at a time per copy of Windows you purchase.

Also (though I've never seen it) if you register an already-registered copy of XP on one computer, the install on the previous computer will cease to work. I've never had any reason to doubt it, but if you don't connect the old computer to the internet, I don't see how they can deactivate the install.

Also, if you don't register, and you reboot when your free time is up, Windows will not start.

What is it they say about silence being golden?