Networks

I've run across a problem to which I have not been able to find a resolution. I have a small network with Windows 2003 (I tried Standard, Enterprise and Small Business versions) with approximately 20 users. The problem appears to have to do with bumping the users off of the network every couple of hours. This problem is very vexing as the users can be in the middle of saving a document, looking for a file to open (using Windows Explorer or IE), playing music files stored on the server or trying to print a document (to the shared printer connected to the server), when the connection is broken. If they use the "Logoff user" and then log back on, all connections are restored (for a period of time) until they are knocked off the network again.
I have checked the Kerberos settings and essentially extended the "disconnect users" function for the 208 day limit, but this does not appear to have made any improvement in the condition.
The users are getting pretty tired of having to logoff and log back on to the network, so I'm beginning to catch some heat over this issue.
Please advise what it is that I am overlooking.
Thanks.