function ImgSwap(imgName, imgSrc)
{
    if (document.images)
    {
      var img = document.images[imgName];
      if (!img) img = ImgFind(document, imgName);
      if (img) img.src = imgSrc;
    }
}

function ImgFind(doc, imgName)
{
  for (var i=0; i < doc.layers.length; i++)
  {
    var img = doc.layers[i].document.images[imgName];
    if (!img) img = ImgFind(doc.layers[i], imgName);
    if (img) return img;
  }
  return null;
}