var theImages = new Array();

theImages[0]  = 'immagini/cartina_1_en.jpg';
theImages[1]  = 'immagini/cartina_2.jpg';

var i = 0;
var p = theImages.length;
var preBuffer = new Array();
for (i = 0; i < p; i++)
{
  preBuffer[i] = new Image();
  preBuffer[i].src = theImages[i];
  // if (preBuffer[i].complete) alert("immagine '" + preBuffer[i].src + "' caricata"); 
}