Using Prototype's CSS-style selectors you can easily track file downloads with Google Analytics:

                      Event.observe(window, 'load', function() {    $$('a[href$=".zip"]', 'a[href$=".pdf"]').each(function(anchor) {
        anchor.observe('click', function(event) {
            if (pageTracker) pageTracker._trackPageview(anchor.getAttribute('href'));
        });
    });
});