The upload file filesystem browser widget is a function of the OS, not the browser, isn't that odd? It gives the browser a way to upload the file, but afaik, it does not mention the path in the POST. So, I think the answer is going to be no: there's no way to let the user browse their file system from your CGI and POST a directory -- without some kind of magic (ie, non CGI.pm) hackery anyway.

UPDATE: "widget is a function of the OS, not the browser" / "No, it's not. It is completely application dependent." Well, the applications I mean are firefox and IE, which load the OS widget, which is why css doesn't work on the file upload buttons. "path in the POST" / "some user agents" So? It's not really something you can depend on then, is it? I think that's not only application dependent, but OS dependent.