var img_cloud = new Array(); 
img_cloud[0] = new Image(); img_cloud[0].src = "img/back_cloud.png"; 

var xi = 0;
function bgGocloud() {
    if(!document.getElementById) return;
    var bcgr = document.getElementById("header");
    bcgr.style.backgroundPosition = 
        xi + "px ";
    xi += 1; if(xi > 1024) xi = 0;
    setTimeout("bgGocloud();", 100);
}