function PopUp(w,h,ziel)
  {
   h = h - 20; var x=0, y=0, parameter="";
   if (w < screen.availWidth || h < screen.availHeight)
    {
     x = (screen.availWidth - w - 12) / 2;
     y = (screen.availHeight - h - 104) / 2;
     if (window.opera) y = 0;
     if (x<0 || y<0)
      {
       x=0; y=0;
      }
     else parameter = "width=" + w + ",height=" + h + ",";
    }
   parameter += "left=" + x + ",top=" + y;
   parameter += ",menubar=no,location=no,toolbar=no,status=no,statusbar=no,resizable=no,scrollbars=yes";
   var Fenster = window.open(ziel,"PopUp",parameter);
   if (Fenster) Fenster.focus();
   return !Fenster;
  }