need help w/ server 2003

I am running Server 2003 as a domain controller and file server. I have one machine that is runing XP Pro and has no problem joing the domain at each login. I am also able to access all shares on the server that this machine has permissions for. The problem is it seems that the session times out. It seems that after awhile (not sure exactly how long) I am no longer able to connect to any share. The only way around this is to either logoff or restart the PC and then it's no problem. Does any one have ne ideas as to what this could be? Could it have something to do with the fact that my screensaver is set NOT to ask for password on resume? Any help would be much appreciated.
Thanx

 

I would start by disabling the power management on the network card.

 

I have disabled power managment on both the server and the client and still it seems after a day or so I have to reboot the client in order to log onto the server. Any more ideas would be great.
thanx