Question : Workgroup is not accessible, cannot browse network.

I have a network of about 50 PCs and a server. OS's are a mix of Win2k and XP Home/Pro.
All are on the same subnet. All use TCP/IP. A few of the workstations had NETBEUI and/or IPX-SPX and those would be viewable at times. I've since removed all other protocols except TCP/IP.

The problem is I cannot browse the network. When I try, I get:

 "WORKGROUP is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.
The list of servers for this workgroup is not currently available"

If I connect any two of the workstations via a crossover cable, I can see them.

What I believe the problem may be is that the server, which is Win2k Advanced Server, is somehow in charge of browsing the network and its not doing its job. I've read that there's a limit to 10 workstations in a workgroup and after that, the server handles the browsing by maintaining a list.

If I'm on the right track by suspecting the server, how might I troubleshoot?

There's no firewall on the server.

Answer : Workgroup is not accessible, cannot browse network.

In a Microsoft network (workgroup or domain), one computer per NetBIOS domain (which is the same as saying "workgroup or domain") will assume the role of "master browser".  All other computers in the NetBIOS domain will look to the master browser for the list of computers on the network.
Now whenever a computer starts up and connects to the network, an election is held to determine which computer on the network would be best suited as the master browser.  Each computer submits its credentials (O/S, processor speed, memory, hard drive space) to each other computer, then each computer "votes" for the most powerful candidate.  This process doesn't take all that long on a small workgroup of up to 10 computers.  It takes even less time on a domain, because every computer in the network knows that the domain controller is the best candidate for master browser, and an election is unnecessary.
In a large workgroup, say 50 computers or so, the problem you'll have is that the election may take a long time, and not every computer may come to the same conclusion as to who the master browser is.  In the confusion of elections, computers (possibly including the master browser or several that think they're the master browser) being turned on or off, and everyone asking everyone else who's really in charge, it's not uncommon for computers to lose track of who's actually on the network, and generate the error message you described.
Now you and I both know that your server should always be getting the master browser role, as it's most likely the most powerful computer in your network.  But unlike us, the rest of your computers don't have any common sense.
So in answer to your question of "what's broken", nothing's really broken.  You've just far exceeded the limits of what a workgroup was really designed to handle.  You may not want a domain, and I can understand that; there are new headaches involved with that, especially during the migration.  But you do need one.  And M$ will probably tell you the same thing; their "official" stance is that any network over 10 computers should have a domain.  (In case you're wondering, I've been an MCSE for 6 years.)