newwindow=false;
function fenster(url,breite,hoehe) {
  if(newwindow&&newwindow.closed==false)
    newwindow.close()
    var l = (screen.availWidth - breite) / 2;
    var t = (screen.availHeight - hoehe) / 2;
    newwindow = window.open(url,"newwindow","width="+breite+",height="+hoehe+",scrollbars=no,left="+l+",top="+t+";");
  newwindow.focus();
}

newwindow=false;
function fensterscroll(url,breite,hoehe) {
  if(newwindow&&newwindow.closed==false)
    newwindow.close()
    var l = (screen.availWidth - breite) / 2;
    var t = (screen.availHeight - hoehe) / 2;
    newwindow = window.open(url,"newwindow","width="+breite+",height="+hoehe+",scrollbars=yes,left="+l+",top="+t+";");
  newwindow.focus();
}