You are definitely having an atypical experience trying to install
your Office 2000. Normally, it installs and runs smoothly with XP.
There should be no reason to have to purchase Office 2003 because of a
problem with you product key. Since your computer is a Dell, there
could even be proprietary software that somehow interferes with your
installation of Office, but this is unlikely. Keep in mind that your
experience is not usual, and I hope the tech support folks you are
paying can help you soon. PS: Have you posted on an Office 2000
newsgroup? They might be the most likely to have encountered your
problem in the past.