codice:
      <script type="text/javascript" language="JavaScript">
      <!--

        var _cxWnd = 100;  // larghezza
        var _cyWnd = 100;  // altezza

        var _xPos  = (screen.width  - _cxWnd) / 2;
        var _yPos  = (screen.height - _cyWnd) / 2;


        window.open( "", "", "height="   + _cyWnd +
                             ",width="   + _cxWnd +
                             ",top="     + _yPos  +
                             ",left="    + _xPos  +
                             ",screenY=" + _yPos  +
                             ",screenX=" + _xPos );

      //-->
      </script>