function popup(ziel,titel,breite,hoehe,werte) {
  if (werte == 'nothing') werte = "location=no,menubar=no,resizable=no,scrollbars=no,status=no,toolbar=no";
  if (werte == 'scroll') werte = "location=no,menubar=no,resizable=no,scrollbars=yes,status=no,toolbar=no";
  if (screen.availWidth <= breite || screen.availHeight <= hoehe) { links = 1; oben = 1; }
  else { links = (screen.availWidth - breite) / 2; oben = (screen.availHeight - hoehe) / 2; }
  fenster=window.open(''+ziel+'',''+titel+'',''+werte+',width='+breite+',height='+hoehe+',left='+links+',top='+oben+'');
  fenster.focus();
}