if (document.images) {  
            img1on = new Image();   img1on.src = "imagenes/principala.gif"; 
            img2on = new Image();   img2on.src = "imagenes/localizaciona.gif";  
            img3on = new Image();   img3on.src = "imagenes/instalacionesa.gif";
            img4on = new Image();   img4on.src = "imagenes/entornoa.gif";
            img5on = new Image();   img5on.src = "imagenes/rutasa.gif"; 
            img6on = new Image();   img6on.src = "imagenes/reservasa.gif";
            img7on = new Image();   img7on.src = "imagenes/descripciona.gif";
            img8on = new Image();   img8on.src = "imagenes/comedora.gif"; 
            img9on = new Image();   img9on.src = "imagenes/habitacionesa.gif";
            img10on = new Image();   img10on.src = "imagenes/luyegoa.gif"; 
            img11on = new Image();   img11on.src = "imagenes/fiestasa.gif";
            img12on = new Image();   img12on.src = "imagenes/piea.gif";                 
            img13on = new Image();   img13on.src = "imagenes/cochea.gif";

            img1off = new Image();   img1off.src = "imagenes/principal.gif"; 
            img2off = new Image();   img2off.src = "imagenes/localizacion.gif";  
            img3off = new Image();   img3off.src = "imagenes/instalaciones.gif";
            img4off = new Image();   img4off.src = "imagenes/entorno.gif";
            img5off = new Image();   img5off.src = "imagenes/rutas.gif"; 
            img6off = new Image();   img6off.src = "imagenes/reservas.gif";
            img7off = new Image();   img7off.src = "imagenes/descripcion.gif";
            img8off = new Image();   img8off.src = "imagenes/comedor.gif"; 
            img9off = new Image();   img9off.src = "imagenes/habitaciones.gif";
            img10off = new Image();   img10off.src = "imagenes/luyego.gif"; 
            img11off = new Image();   img11off.src = "imagenes/fiestas.gif";
            img12off = new Image();   img12off.src = "imagenes/pie.gif";
            img13off = new Image();   img13off.src = "imagenes/coche.gif";
        }

    function imgOn(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "on.src");       
            }
    }

    function imgOff(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "off.src");        
            }
    }