function rollover(obj) {
	var str = obj.id + "Button";

	var imgObj=document.getElementById(str);
	var imgSrc = imgObj.src;
	if (imgSrc.indexOf("_on") == -1) {
		imgObj.src = imgSrc.replace("_off", "_on");
	} else {
    	imgObj.src = imgSrc.replace("_on", "_off");
	}
}