nombre = navigator.appName;
version = parseInt(navigator.appVersion);

if ((nombre == "Netscape" && version >= 3) || (nombre == "Microsoft Internet Explorer" && version > 3)) 
ver = "correcta";
        else ver = "incorrecta";

if (ver == "correcta") {

espa = new Image();
espa.src = "images/icon_es.gif";
espb = new Image();
espb.src = "images/icon_es_on.gif";

fraa = new Image();
fraa.src = "images/icon_fr.gif";
frab = new Image();
frab.src = "images/icon_fr_on.gif";

enga = new Image();
enga.src = "images/icon_en.gif";
engb = new Image();
engb.src = "images/icon_en_on.gif";

}

function abajo(imgName) {
        if (ver == "correcta") {
        document[imgName].src = eval(imgName + "a.src");
}
}
function arriba(imgName) {
        if (ver == "correcta") {
        document[imgName].src = eval(imgName + "b.src");
}
}