Why Is This Happening?

I have recently upgraded to Windows XP Home Edition.
From time to time a window pops up that tells me that it
is trying to install Office 2000. The bar shows that
something is being loaded for a few moments, then another
window opens that tells me that the feature that I am
trying to use is not available, please insert your Office
2000 disk into the drive.

This appears to happen randomly and at times that I am
not aware that I am trying to use an Office 2000
feature. For example, this last occured when I
attempeted to search for a file using the search
feature. I have had Office 2000 installed for several
years and never had this happen when I was using Windows
98SE.

So far this appears to only be an annoyance, but I would
like to know what is going on.