Authentication seems to time out

I’m working with a Win2k Server/AD with approx 10 XP Pro workstation clients and one Fiery Print Server. WS uses DHCP from DSL router and Static IP assigned to Fiery. Clients Can Connect to any WS, Fiery and Server immediately after logon, however after approx 15-30 minutes WS can’t browse the network or connect to Fiery to print, but can connect to Server, Dialog box asks for user name and password, have to put in different user info to reconnect, then times out again, if user logs off/on, then can reconnect for short time. I suspect it is a DNS problem but I haven’t investigated that as yet, I inherited this situation and am looking for any suggestion that might apply. Should I enable WINS and do NET BIOS resolutions? thank you..