function smartRollover() {
	
	if(document.getElementId) { return; }
	
	var images = document.getElementsByTagName("img");
	var aPreLoad = new Array();
	
	for(var i=0; i < images.length; i++) {
		if(images[i].getAttribute("src").match("_off.")){
			aPreLoad[i] = new Image();
			aPreLoad[i].src = images[i].getAttribute("src").replace("_off.", "_on.");
			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);
}