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

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

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