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") {

homa = new Image();
homa.src = "images/bot_home_in.gif";
homb = new Image();
homb.src = "images/bot_home.gif";

mapa = new Image();
mapa.src = "images/bot_map_in.gif";
mapb = new Image();
mapb.src = "images/bot_map.gif";

infa = new Image();
infa.src = "images/bot_info_in.gif";
infb = new Image();
infb.src = "images/bot_info.gif";

zpra = new Image();
zpra.src = "images/bot_llave_in.gif";
zprb = new Image();
zprb.src = "images/bot_llave.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");
}
}