var image = new Object();

function preloadImage(name, state, src)
{
  if (!image[name]) image[name] = new Object();
  image[name][state] = new Image();
  image[name][state].src = src;
}

function swapImageById(img, name, state)
{
  if (image[name])
  {
    img = document.images[img];
    img.src = image[name][state].src;
  }
}