Missing PCs on domain

I inhereted a small NT4.0 SP6 domain with 15 NT 4.0 SP4 (or better) workstations and 1 WIN2K w/s. Nearly half of the w/s (includieng WIN2K box) do not appear in Network Neighborhood. All have workstation service enabled. When missing PCs are doubleclicked in Server Mgr, the stop message “The network path was not found.” appears. I can ping all workstations and all have access to server resources. Netwatch tracks them fine