function smartRollover() {
        if(document.getElementsByTagName) {
            var images = document.getElementsByTagName("img");

            for(var i=0; i < images.length; i++) {
                if(images[i].getAttribute("src").match("_off."))
                {
                    images[i].onmouseover = function() {
                        this.setAttribute("src", this.getAttribute("src").replace("_off.", "_on."));
                    }
                    images[i].onmouseout = function() {
                        this.setAttribute("src", this.getAttribute("src").replace("_on.", "_off."));
                    }
                }
            }
        }
    }

    if(window.addEventListener) {
        window.addEventListener("load", smartRollover, false);
    }
    else if(window.attachEvent) {
        window.attachEvent("onload", smartRollover);
    }