Need help with network setup

Ok, so first, here is the setup.

1 Linksys 5 port Cable/DSL router
1 SMC 16 port switch
1 Windows 2003 Server Basic
4 Windows XP Workstations

I inherited this job from another company and have made it work fairly well, but I keep running into a problem. The Linksys router appears to be causing a slow down of network traffic. The server responds to requests, but very slowly. Logging in takes easily 5 minutes. If I remove the router from the picture, things go fine. If I shut down the server, everything else runs at normal speed. I’m thinking that the router wants to manage DNS, DHCP and such and the server is not playing nicely with that which is what is causing the slow downs. I need some ideas on what to change in order to make this go at relatively decent speeds when accessing the server.