var img_width = "780";
var img_height = "80";

var ad=new Array()
//insert here your images src
ad[0]='http://www.sunvar.com.ph/images/ads/1.jpg';
ad[1]='http://www.sunvar.com.ph/images/ads/2.jpg';
ad[2]='http://www.sunvar.com.ph/images/ads/3.jpg';
ad[3]='http://www.sunvar.com.ph/images/ads/4.jpg';

var xy=Math.floor(Math.random()*ad.length);
document.write('<img src="'+ad[xy]+'" width="'+img_width+'" height="'+img_height+'" alt="">');