function switchImage(imgName, imgSrc) 
{
  if (document.images)
  {
    if (imgSrc != "none")
    {
      document.images[imgName].src = imgSrc;
    }
  }
}

// Example:
//simplePreload( 'picts/statelocal250c.jpg', 'picts/education250c.jpg', 'picts/federal250c.jpg', 'picts/commercial250c.jpg' ); 
function simplePreload()
{ 
  var args = simplePreload.arguments;
  document.imageArray = new Array(args.length);
  for(var i=0; i<args.length; i++)
  {
    document.imageArray[i] = new Image;
    document.imageArray[i].src = args[i];
  }
}