Hover = {
    add: function(elementId, hoverSrc, outSrc) {
        var element = $(elementId);

        Event.observe(element, 'mouseover', function() {
            element.writeAttribute('src', hoverSrc);
        });
        Event.observe(element, 'mouseout', function() {
            element.writeAttribute('src', outSrc);
        });
    }
}