Workstations locking up

We have two clients running Server2003 and they have certain windows XP SP2
workstations that slow down and/or lockup between 4:30 and 5:30 PM each day.
There is nothing in the logs that shows a problem accessing the network data,
or any application errors on either the server or workstations. I am looking
for all ideas to what the problem may be. Or, any ideas on how to trouble
the shoot the problem.

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Eric Speake. MCSE, CCNA
Harmon Systems Inc