var imglist =  new Array(
      "http://www.silkfield.com/image/top_image01.jpg",
      "http://www.silkfield.com/image/top_image02.jpg",
      "http://www.silkfield.com/image/top_image03.jpg",
      "http://www.silkfield.com/image/top_image04.jpg",
      "http://www.silkfield.com/image/top_image05.jpg");
   var selectnum = Math.floor((Math.random() * 100)) % imglist.length;
   var output = "<img src='" + imglist[selectnum] +"' width='634' height='256' border='0'>";
   document.write(output);