machines not showing up in Network Neighborhood

We have a domain of approximately 250 Windows XP workstations, with
2 Windows 2003 Servers as domain controllers. The workstations are
spread over 3 student labs, many desktop machines, and some laptops.
Two of the student labs are in remote buildings.

Our problem is that the 48 machines that are in the student lab that
is in the same building as the domain controllers, on the same IP
subnet, are not showing up in Network Neighborhood. All other machines
in the domain show up, including those in the remote student labs, one
of which is on a separate IP subnet.

Strangely, this seemed to happen slowly over time, with machines
dropping off one by one until now none of them show up. The machines
can be pinged, and I can log on to them remotely, and they are getting
updates, etc. In other words, nothing seems to be wrong with the
connections, they just do not show up in Network Neighborhood.

This is a mystery I would like to solve for its own sake, but also
because machines that don't show up in Network Neighborhood, also do
not show up in the Sophos Enterprise Manager's SAVAdmin, which is
what we use to monitor the status of our virus checking software.
I cannot push a configuration to those machines.

I am at a loss as to what the problem might be. Can anyone give me
ideas as to what to look for?

TIA,
Sandy

--
Sandra L Miller
Windows System Administrator
Department of Computer Science
University of Arizona

"The opinions or statements expressed herein are my own and should not be
taken as a position, opinion, or endorsement of the University of Arizona."