if (document.getElementById) { window.onload = swap };

function swap() {
var numimages=10;
rndimg = new Array("images/header_home1.jpg", "images/header_home2.jpg", "images/header_home3.jpg", "images/header_home4.jpg", "images/header_home5.jpg", "images/header_home6.jpg", "images/header_home7.jpg", "images/header_home8.jpg", "images/header_home9.jpg", "images/header_home.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("banner").style.backgroundImage = "url("+ randomimage +")"; 
}