I think you are correct, the one computer has no way of seeing the other one then. Though I have no experience with work groups, they might be able to see other users. I keep running through possibilities in my head and they all have to do with one computer being able to see the users on the other (like changing the iis service to run as the user you used to map the network share) and I can't think of a way to get this to work at the moment if the computers can't see each other's users. sorry.
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