lol...u guys dint get his problem...
the CD key was working for WinXP "gold" version...
but its not working with WinXP "SP2" version (since he got that slipstreamed)
and afaik, microsoft blacklisted some illegit CD keys in SP2
as it turns out his original (assumed) CD key falls within that range.
and getting the CD key frm register wont help either.
the only option to do smthing legally is to contact microsoft support
and explain to them the problem or get a new cd key frm them.