Hi, confused,
If you look in Add/Remove Programs in the Windows control panel does it show
MS Office XP Professional (which uses PRORET.MSI) or MS Office XP
Professional with FrontPage (which uses PROPLUS.MSI)?
The MS Installer is expecting to find a matched set of the original
installation CD and location.
If they don't match try uninstalling the one you have and then installing
the one you do prior to updating so you'll have the matched set.