XP losing domain access

Recently after installing one of MS many 'security' updates, I now find
that our XP workstations can no longer access certain servers on the
domain without having to 're-login' to that particular server. I can't
quite put my finger on the timeout interval, but it appears to be
around 15 minutes or so.

The servers in question are all running Server 2003 and the
workstations are all XP-SP2. The connections are on a single backbone
and the XP firewall has been disabled. The workstation IP addresses
are assigned via DHCP and are all private. Power configuration for all
systems is Always On. Can't think of anything else which might affect
the connection. I also don't recall ever experiencing this problem
prior to the updates loaded within the last month. It isn't viable to
uninstall them at this time.

The current configuration is two domains, one 2003 with ASD and one NT4
with reciprocal trust relationships. The problem occurs within the
2003 domain - both the workstations and the servers are on the same
domain. The workstation is currently logging in using a user ID with
administrative access rights, and when the workstation first boots up
and logs in, it sees and can access the servers with no problems
through Win Explorer, My Network Places, Entire Network, Microsoft
Windows Network, XDomain, ServerA. After 15 minutes or so, clicking on
ServerA (which is still visible in the list even after refreshing)
brings a long wait, followed by a dialog window with the "Connect
as..." user ID and password prompt.

I've searched everywhere but while some topics allude to timeout
parameters, I cannot seem to locate anything which addresses this
particular problem nor how to configure a parameter short of editing
the registry.

Ideas/suggestions?