This worked for me.

[Jim]

I was having the same problems installing updates, etc.
as many others seem to be having. Also I was unable to
uninstall Office 2000 Small Business because it said my
Windows Installer program was missing. On CD #1 I opened
a folder named MSI then clicked a file named INSTMSIW.
This allowed me to uninstall MS Office and then reinstall
it from scratch. While installing SP3 and some other
updates a "problem" box popped up several times but I
clicked Ignore and it proceeded with the installation.
Hope this helps.