caveat: I have never used Selenium, nor the module you mention

1. Correct me if I'm wrong, but if you 'get_page_source', it's essentially going to be HTML. Perhaps the zip file will be embedded in it (although I doubt it), but it's going to have formatting around it. Have you looked at the file after you copied it? Checked the size?
2. Is there some reason why you chose Selenium to do this? It's more of a test/validation tool.
3. Did you look at WWW::Mechanize? The 'get' method should give you the file the way you want it

fnord