Look at the Windows System Monitor on each machine in order to locate the bottleneck. Some possible performance metrics to look at are:
Network InterfaceCurrent Bandwidth
Network InterfaceBytes Total/Sec
Processor% Processor Time
Physical DiskAvg. Queue Length Time
These and other system counters will allow you to decide if you need to upgrade or replace any equipment, or alert you to potentially "chattering" or malfunctioning devices.
This was first published in June 2004