function cbonline_popup() {

    var w = 640;
    var h = 480;

    w = screen.availWidth;
    h = screen.availHeight;

    var popW = 840;
    var popH = 650;

    var leftPos = (w-popW)/2;
    var topPos = (h-popH)/2;

    window.open ("http://www.cbonline.org.au/info","CBOnline","menubar=no,width=840,height=650,toolbar=no,screenX="+leftPos+",scrrenY="+topPos);

  }