I just was puttering around with a few VM's. I changed workgroups around and for those that did not have Computer Browser running, did not see each other with a scan. When I fired it up, it showed them.
Let me add one footnote to my earlier comment. It would be 'Best Practice' to have all of the computers in the same workgroup, but it is not a requirement 'Unless you are on WindowsME' :-P