When using Samba PDC with Samba WINS server the PDC lists all domains registered with the WINS Server in the browse.dat file. When using Samba PDC with W2K WINS server additional domains are not added to the browse.dat file. This results in the other domains not being listed in the Network Neighborhood without editing the registry file on each and every client.
Sounds like a bug in the Win2k wins server, not Samba.