// Function to 'activate' images.
function imgOn(imgName) 
{
  if (document.images) 
  {
    document[imgName].src = eval(imgName + "on.src");
  }
}

// Function to 'deactivate' images.
function imgOff(imgName) 
{
  if (document.images) 
  {
    document[imgName].src = eval(imgName + "off.src");
  }
}