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);
}else if(document.getElementById){
    window.onload=smartRollover;
}