Microsoft Office 2000 Professional Product Key Issue

I have Microsoft Office 2000 Professional(original discs x2). I believe I have the original product key, yet when trying to re-install coming back as incorrect key. I believe that a new key was issued/acertained when major update 02ksr1a was incorporated. Although, this problem has only arisen after I trialed Office 2007 – decided not for me and then tried to re-install Office 2000. Contacted M/Soft Helpdesk and was given new product key/s, yet still did not work. Can anyone advise me on solution/way forward for re-installing Office2000