function setBackgroundImage (id) {
	// Randomly select image
	var numbOfPics = 4;
	var randomNumb = Math.ceil (1000 * Math.random ());
	var pictureIndex = (randomNumb % numbOfPics) + 1;
	var imageURL = 'graphics/u-side--0' + pictureIndex + '.gif'
	
  if (document.layers)
    document[id].background.src = imageURL;
  else if (document.all)
    document.all[id].style.backgroundImage = 'url(' + imageURL + ')';
  else if (document.getElementById)
    document.getElementById(id).style.backgroundImage = 'url(' + imageURL + ')';
}