XP and 2k AS Networking problems please help

[Nosdivra]

I am working in an office with 3 XP machines and 1 2000 advanced server. The problem is after a day the XP machines start responding really slow. Files are stored on the server and when you click on the open or save buttons it can take up to a minute or more to finally come up with the open or save window. Internet Explorer can take minute or 2 to open up. The whole PC slows down. The server is fine its just the xp machines. XP's are running wordperfect office 11. Server has all the data, Tapeware Administrator, and Norton Small Business Edition Anti-virus. Tapeware is schedualed to run at night but only backs up the server. Norton is running on Sunday. I have removed Norton, replaced Motherboard and CPU, replced the switch. I dont know what else is wrong. I have searched microsofts website i found a tech help issue with XP, Norton realtime virus check and a hot fix but the hot fix has since been removed and still having slow issuses.

[DVNT1]

Is this setup as a Domain or Workgroup?

Have you checked the processor usage via Task Manager (looking for anything that is using a very high processor percentage)?

[Nosdivra]

Domain and yes.