Event.observe(window, 'load', function () {
    $A($('menu').getElementsByTagName('img')).each(function (el) {
        el.imgs = [new Image(), new Image()]
        el.imgs[0].src = el.src
        el.imgs[1].src = el.src.replace(
                '/menu-normal/', '/menu-highlight/')
        
        el.onmouseover = function () { el.src = el.imgs[1].src }
        el.onmouseout = function () { el.src = el.imgs[0].src }
    })
}, false)