var theImages = new Array();

theImages[0] = 'images/wallpaper2.jpg';
theImages[1] = 'images/wallpaper3.jpg';
theImages[2] = 'images/wallpaper4.jpg';

var p = theImages.length;
var whichImage = Math.round(Math.random()*(p-1));

function rnd_wallpaper(BaseUrl) {
	document.getElementById("header_img").style.backgroundImage = "url(" + BaseUrl + theImages[whichImage] + ")";
}