Do you have your original disks?
This solution was supplied by Jay Freedman, Word MVP
In Control Panel > Add/Remove Programs, select the Office 2003 entry
and click the Change button. In the dialog, select "Reinstall or
Repair" and click OK. Eventually it will ask for the original
distribution CD or DVD disk. Put the disk in the drive and let it
finish.
The explanation is that something (a dll or a registry entry) is
damaged in your Office suite, and the cached copy of the installer
files either is also damaged or has been removed. That's why it needs
the original disk. SKU011.CAB happens to be the first file the
installer needs to read -- if you supplied only that one file, then
the installer would ask for whatever comes next.