function OpenPopup ( URL, NAME, ANCHO, ALTO ) {

          var izquierda = (screen.width) ? ( screen.width - parseInt ( ANCHO ) )/2 : 100;
	     var arriba = (screen.height) ? ( screen.height - parseInt ( ALTO ) ) /2 : 100;

          var PARAMETROS = 'channelmode=0,dependent=0,directories=0,fullscreen=0,location=0,menubar=0,';
             PARAMETROS += 'resizable=0,scrollbars=0,status=0,toolbar=0,titlebar=0,';
             PARAMETROS += 'width=' + ANCHO + ',height=' + ALTO + ',left=' + izquierda + ',top=' + arriba;        

        window.open(URL, NAME, PARAMETROS);  

     }