function setNavImage() {
  docname = document.location.href;

  if(docname.lastIndexOf("/") == docname.length-1) {
   docname = "index";
  } else {
    s = docname.lastIndexOf("/");
    e = docname.lastIndexOf(".");
    docname = docname.substring(s+1, e);
  }
  ById('nav_'+docname).src="images/i-nav-"+docname+"-current.gif";

}

//document.body.onload = setNavImage();
document.onload = setNavImage();

function ById(id) {
  return (document.getElementById && document.getElementById(id)) ? document.getElementById(id) : false;
}