Samba and Win 2k problem

Hi, I have SuSE Linux 7.0 box with Samba + sevaral Mac and PC workstations. After upgrading from Win98 to Win2k on 3 pcs they stopped to work with Samba. In fact, Samba server is not visible anymore neither in 'My Network Places -> Computers near me" neither in "Entire Network -> My Workgroup". No network settings have been changed, and I do not have NT Domain server whatsoever. I suspect something is wrong with tonneling of NetBIOS through TCP/IP, but could not figure out what. Thanks for any suggestions. Andrei