var preloadImages = new Array();
        doRollover = function(thisel) {
                var src = thisel.getAttribute('src');
                src = src.replace('-on','');
                var extension = src.substring(src.lastIndexOf('.'),src.length);
                var nsrc = src.replace(extension, '-on'+extension);
                var oFun = function(nsrc) { return function() { this.src = nsrc; } };
                thisel.onmouseover = oFun(nsrc);
                thisel.onmouseout =  oFun(src);
                var preImg = new Image();
                preImg.src = nsrc;
                preloadImages[preloadImages.length] = preImg;
        };