function pop(url,breite,hoehe)    {
      var pop = null;
      pop =  window.open(url,'popwin','width='+breite+',height='+hoehe+',resizable=no,status=no,scrollbars=no,menubar=no,toolbar=no,directories=no')
      if (pop) {
         pop.moveTo(screen.width/2-breite/2,screen.height/2-hoehe/2);
         pop.window.focus();
      }
}