function pop(url,w,h, n){
  var l = (self.screenLeft + ((document.body.offsetWidth-4)/2)) - (w / 2);
  var t = (self.screenTop + ((document.body.offsetHeight-4)/2)) - (h / 2);
  var v = ",left=" + l + ",top=" + t;
  
  newwindow = window.open (url, n, "status=no,toolbar=no,location=no,menubar=no,scrollbars=no,resizable=yes,width=" + w + ",height=" + h + v);
}