Workgroup not accessible in XP

I have searched the Internet and found dozens of cases of this, and tried
several suggestions without success.

I have a home LAN of four computers, three XP and one ME, accessing the
Internet and each other via an Origo ADSL modem/router/switch.

They all have the same workgroup name, and all have Norton Personal Firewall
installed.

Most of the time when I access the workgroup on my main computer, via 'My
Network Places', etc, it gives the error message 'Workgroup is not
accessible. You may not have permission to use this network resource.' It
will not even display its own name. If I retry a few times I get a blank
window for the workgroup contents. Even if I disable the LAN connection, so
no other machines should be found, it fails in the same way.

Occasionally it works perfectly, so I can't believe I have something
configured wrongly.

I have tried configuring and disabling the firewalls and all sorts of other
suggestions I have found online, but I can't make it work consistently.

Is there a solution or do I have to live with it?

--
Chris Melluish