Using firefox's "save target as" feature, you can get round web authentication.

Make a password protected directory (with a video file inside) (using .htaccess and htpasswd), check that it actully requires a login when you click the link to the video normally, then create a hyperlink to the file, right click save as - oh snap, it doesn't ask for authentication.

I've only tested it with a video file and Firefox 1.0.6.