Hi, Al.
Do you really mean "register"? Or do you mean "activate"? BIG difference!
Register just tells Microsoft your name and address so they can put you in
their database and keep you informed of future "good deals". Registering is
entirely voluntary on your part.
Activation, though, is Microsoft's way of enforcing their EULA (End User
License Agreement) that we all must agree to in order to get the license to
actually use Windows. Without that, we may have the "bits" on our computer,
but we are not legally entitled to run and use WinXP. The EULA is
essentially the same as always - one Windows license for each computer - but
now it is being enforced.
If your used computer originally came with WinXP pre-installed, then it has
already been activated and you should not have to do anything. (You may
want to register your ownership, but that's voluntary, as I said.) If the
prior owner bought a retail version of WinXP and installed it, he should
have already activated it, and you need not activate it again. If he had
not yet activated WinXP, he should have furnished you with the WinXP CD-ROM;
on the CD-ROM case there should be a bright orange sticker with your Product
Key and the warning, "Don't Lose This Product Key!" When WinXP prompts you
to activate, use this key to do that. The easiest way is to activate it
through the Internet, but if that fails for any reason, you should see
instructions to call a toll-free number (which will be furnished); this is
usually a painless 5-minute procedure.
For the full details on WPA (Windows Product Activation), go here:
http://www.microsoft.com/piracy/basics/activation/
RC