var nav = navigator
browserIE = ((nav.appName == "Microsoft Internet Explorer") && (parseInt(nav.appVersion) >= 4 ))
browserNS1 = ((nav.appName == "Netscape") && (parseInt(nav.appVersion) < 5 ) ) // Netscape < 4.7
browserNS2 = ((nav.appName == "Netscape") && (parseInt(nav.appVersion) >= 5 ) )// Netscape >= 6

// Precarga de imágenes ----------------------------------------
var i;
var imagenes = new Array("images/menu/que.gif","images/menu/que2.gif","images/menu/centro.gif","images/menu/centro-2.gif","images/menu/distribuidor.gif","images/menu/distribuidor-2.gif","images/menu/vehiculo.gif","images/menu/vehiculo-2.gif","images/menu/contactar.gif","images/menu/contactar-2.gif");
var lista_imagenes = new Array();
function cargarimagenes(){
for(i in imagenes){
lista_imagenes[i] = new Image();
lista_imagenes[i].src = imagenes[i];
}
}

function cambio(nombre,index){
  if ((browserIE)||(browserNS2))
  {
      document.images[nombre].src = lista_imagenes[parseInt(index)].src;
  }
  else if (browserNS1)
  {
      document.layers["menu"].document.images[nombre].src = lista_imagenes[parseInt(index)].src;
  }
}