ranimg = new Array(); 
ranimg[0]="index.files/top001.jpg"; 
ranimg[1]="index.files/top002.jpg"; 
ranimg[2]="index.files/top003.jpg"; 
ranimg[3]="index.files/top004.jpg"; 
xx = Math.floor(ranimg.length*Math.random()); 
ranimg = ranimg[Math.floor(xx)]; 
document.write ('<style type="text/css"><!--.random {background-image: url("'+ ranimg +'");background-position: center;}--></style>');