ranimg = new Array();
ranimg[0]="001.jpg";
ranimg[1]="002.jpg";
ranimg[2]="003.jpg";
ranimg[3]="004.jpg";

xx = Math.floor(ranimg.length*Math.random());
ranimg = ranimg[Math.floor(xx)];
document.write ('<style type="text/css"><!--body {background-image: url("'+ ranimg +'");background-repeat: no-repeat;background-position:40px 60px;}--></style>');