function popup(datei,hoehe,breite,win_name) {
 new_left = (screen.width-breite)/2;
 new_top  = (screen.height-hoehe)/2;
 var popup = window.open(datei,win_name, "height=400, width=" + breite + ",top=" + new_top + ",left=" + new_left + ",resizeable=no");
 popup.focus();
}