Is this M$ Network Neighborhood stuff? I didn't know about this 'feature' until I read this node, but I would assume this doesn't actually involve HTTP, does it?
My guess is that since Windoze treats Network Neighborhood files/folders as local, when you type "file://..." the browser is only going to the OS ( i.e., not network activity from the browser's perspective) to ask for the file, thinking that is a local file?
If so, the reason why LWP fails to find these files is because LWP tries to talk HTTP to find the files on the peer machine, and since a regular Windoze workstation don't come with an HTTP server, the attempt fails.
I don't have ActivePerl installed on my Win2k so I can't try it, but I'd almost think that on a Network Neighborhood - equipped Win box, you can achieve the same effect by using a regular file open() ? Just a wild guess.