Event.observe(window, 'load', function() {

    //automatic rollovers
    $$('img').each(function (e) {
        var over = e.readAttribute('oversrc');
        if (over != null) {
            var oldsrc = e.src;
            e.observe('mouseover', function(x) {e.src = over});
            e.observe('mouseout', function(x) {e.src = oldsrc});
        }
    });

});