Lost network connectivity

I recently replaced my desktop computer with a new PC running XP Pro. I connect to a Windows 2000 domain controller. I leave the computer running. Every morning, I lose access to mapped drives and shared printers on the network. Internet access is fine. I can ping all stations on the net. Logging off and logging back in resolves the problem. I have changed net cards and updated Windows with no positive results. Any ideas would be greatly appreciated.