Network Slowdown

I have a problem that you maybe able to assist me with. We have a Network consisting of a Win2k3 Server and 3 workstations. The Server shares a Folder that is mapped as F:\. The system works fine until one of the workstations shuts down. After it shuts down the network slows down dramatically. I checked if any thing is shared on the workstation but nothing was, and all users have a log on script that disconnects and reconnects their F:\.
Any ideas what could cause this?