Upgrading Vista Business to Vista Enterprise Removed programs?

We purchase our computers from Dell with Vista Business on them. We then use
our Volume License Key (MAK) and upgrade them to Vista Enterprise. When we
upgraded them to Vista Enterprise they lost their Active Directory Users and
Computers program that had been installed. I didn't think an upgrade would
remove installed programs. Is this expected behavior?

Thank you.

I can't speak for your situation with OEM installation and using a MAK
but I did upgrade my VISTA Business installation which was from the RTM
disk to VISTA Ultimate but I used a full copy of Ultimate and not an
Upgrade version. I did not lose applications I had installed under
Business or data.

It did take a few hours compared with the 40 minutes of the first clean
install.