function PopUp(w,h,ziel) {
  h = h - 20; var x=0, y=0, parameter="";
  if (w < screen.availWidth || h < screen.availHeight) {
    x = (screen.availWidth - w - 12) / 2;
    y = (screen.availHeight - h - 104) / 2;
    if (window.opera) y = 0; // Opera positioniert unter den Symbolleisten
    if (x<0 || y<0) { x=0; y=0; }
    else parameter = "width="+w+",height="+h+",";
  }
  parameter += "left=" + x + ",top=" + y;
  parameter += ",menubar=no,location=no,toolbar=no,statusbar=no";
  parameter += ",resizable=yes,scrollbars=no";
  var Fenster = window.open(ziel,"PopUp",parameter);
  if (Fenster) Fenster.focus();
  return !Fenster;
}