OK, thanks Steve, I knew it was using a standard Windows function… There do seem to be different ones out there, for example some allow you to see and use Windows shortcuts, others (like BrowseForFolder) they do not show up…
Anyway, I worked around it by providing the user an alternative stringbox for the path. That way one can use Windows Explorer (outside of Rhino) to browse to the folder on the newwork, click in the path box and extract the full path to the folder, and paste it into the stringbox in Rhino… Not exactly elegant, but it works… 
–Mitch