function popup(url, x, y) {
    var ww=(screen.availWidth-x)/2;
    var wh=(screen.availHeight-y)/2;
    window.open(url, "", "width="+x+", height="+y+", top="+wh+", left="+ww+", screenX="+ww+", screenY="+wh+", status=no, scrollbars=no, resize=no");
}