img = new Array();

img[0] = "http://www.preciouz.com/wp01/images/top01.jpg";
img[1] = "http://www.preciouz.com/wp01/images/top02.jpg";
img[2] = "http://www.preciouz.com/wp01/images/top03.jpg";
img[3] = "http://www.preciouz.com/wp01/images/top04.jpg";
img[4] = "http://www.preciouz.com/wp01/images/top05.jpg";

n = Math.floor(Math.random()*img.length);

document.write("<img src='"+img[n]+"' border='0' alt='' width='640' height='480' class='aligncenter' />");