You can add Public folder functionality to any file or folder. See http://www.dropbox.com/help/167

No, you can't, because that generates one-off links with gibberish in the URL and forces the disposition to "download" instead of just sending the file.

no, it isn't. just has to be manually enabled.

http://forums.dropbox.com/topic.php?id=62403&replies=10#...