function AddLink() {
   var w = 400;
   var h = 350;
   var l = Math.floor((screen.width-w)/2);
   var t = Math.floor((screen.height-h)/2);
      window.open("add_link.php","","scrollbars=1,width=" + w + ",height=" + h + ",top=" + t + ",left=" + l);
 }