I used to have as a file server for my clients recently and switched to windows server 2008 and I faced strange problem My win7 clients have no problem but xp client get disconnected about 2-3 time a day. I had not any problem when I had server2003, this problem starts when I changed my server from 2003 to 2008, be sure that the is no any network problem, ping in both side are under 1ms
Please check through Windows Server 2008 does not use CIFS to connect to network shares (and sublinks there) for possible causes and solutions.
which basically tells that you must have WINS server (or dynamic DNS) server.
From my experience, I cannot see my own PC in "My Network Places" in WindowsExplorer without WINS