function popup(url,breite,hoehe,pos){
    if(isNaN(breite))breite=400;
    if(isNaN(hoehe))hoehe=400;

    if(pos=="right"){
        oben=24;
        links=window.screenLeft+document.body.offsetWidth;
        if(links+breite>screen.width)links=screen.width-breite-12;
    }
    else{
        if(pos=="left"){
            oben=0;
            links=0;
        }
        else{
            oben=screen.height/2-hoehe/2;
            links=screen.width/2-breite/2 - 12;
        }
    }
    windowprops = "height="+hoehe+",width="+breite+",left="+links+",top="+oben
                + "location=no,scrollbars=yes,menubars=no,toolbars=no,resizable=yes,status=no";

    lotzkat_popup = window.open(url, "lotzkat_popup", windowprops);
    lotzkat_popup.focus();
    return false;
}