samba - Sep 2001 - Samba 2.0.7 not visible in browse list on _some_ W2K machines

I installed a Samba 2.0.7 system on FreeBSD 4.2 earlier this year.
The client has been adding new clients to the system during the
course of the year and now we're suddenly having some trouble.
_some_ of the W2K machines don't see the server in the browse
list.  We can map drives just fine by entering the netbios name
(i.e. "net use e: \\server\share") but the server doesn't show
up on the browse lists.  All other netbios computers show up.
All the NT4 machines, and one of the W2K machines work perfectly,
but 4 out of 4 new W2K machines have this problem.  The browse
list shows all the other NT4 and W2K machines, but the Samba server
is missing.
We're using workgroup-style security, and all machines are in the
same workgroup.  The Samba server is acting as a WINS server.

Anyone seen this? Any suggestions? Is an upgrade in order? I don't
have a problem upgrading to a new version of Samba, but I don't
want to do it if it's not the solution.

TIA,
Bill Moran
-- 
"Where's the robot to pat you on the back?"