var img_id = 1

function init_alter() {
  setTimeout("alternate_image()",4000);
} 

function alternate_image() {
  img = getElement("frim"+img_id);
  fade("frim"+img_id);
  img_id = img_id == 3 ? 1 : (img_id + 1);
  //img.src = "/img?db=front&id=" + img_id;
  appear("frim"+img_id);
  setTimeout("alternate_image()",4000);
}

addLoadEvent(init_alter);