CD required for updates of newer version

We had MS Office 2000 installed on computers running Windows XP pro sp2 and we have upgraded to MS Office 2003. When I installed the new version it gave me the option of removing the old version of Office and I chose it but when I updated office 2003 after the install was finished it asked for the CD from Office 2000 and it wouldn’t update until I put that CD in. Why, and how do I fix it? I don’t care if it asks for the Office 2003 CD because I copied it to most of the computers before I installed it so I would not have to carry around the CDs.