var image = new Array();
 image[0] = '/images/layout/header01.jpg'; 
 image[1] = '/images/layout/header02.jpg'; 
 image[2] = '/images/layout/header03.jpg'; 
 image[3] = '/images/layout/header06.jpg'; 
 image[4] = '/images/layout/header07.jpg'; 

var index = Math.floor(Math.random() * image.length);
document.write('<style type="text/css"> #header { background-image: url('+ image[index] +'); background-repeat:no-repeat;}  </style>');