This forum is reserved for feedback concerning the forums themselves. Your question would be best addressed in the Windows XP forum.

In regards to the question itself, there is no simple answer. The problem is that without the certificate of authenticity, original Windows CDs, etc you don't really have a basis for arguing its legitimacy to Microsoft. You could go here for the 'official' validation page, but if your copy turns out to be invalid you're left with either purchasing a legal license to Windows or choosing a free Linux distro such as Ubuntu.

Sorry.
John