function oeffnefenster (url) {
 var w=700;
 var h=650;
  var padding;
    (navigator.appName == "Microsoft Internet Explorer") ? (padding = 10) : (padding = 0);

    var screenw = screen.availWidth;
    var screenh = screen.availHeight;
    var winw = (w + 15 + padding);
    var winh = (h + 15 + padding);
    var posx = (screenw / 2) - (winw / 2);
    var posy = (screenh / 2) - (winh / 2);
 
 fenster=window.open(url, "_blank","top="+posy+",left="+posx+",width="+w+",height="+h+",menubar=no,locationbar=no,statusbar=no,resizable=no,toolbar=no,dependent=yes,scrollbars=no");
 fenster.focus();
 return false;
}