function popup(url, width, height)
{
  wx = (screen.availWidth - width)/2;
  wy = (screen.availHeight - height)/2;

  return window.open(url, "_blank", "width="+width+",height="+height+",status=no,resizable=0,scrollbars=1,toolbar=no,menubar=no,left="+wx+",top="+wy);
}