function showPic(whichpic) {
  if (!document.getElementById("illu_img")) return true;
  var source = whichpic.getAttribute("href");
  var illu_img = document.getElementById("illu_img");
  illu_img.setAttribute("src",source);
  return false;
}
function clearPic() {
  if (!document.getElementById("illu_img")) return true;
  var illu_img = document.getElementById("illu_img");
  illu_img.setAttribute("src","medias/illu_accueil.jpg");
  return false;
}
function prepareGallery() {
  if (!document.getElementsByTagName) return false;
  if (!document.getElementById) return false;
  if (!document.getElementById("menu_accueil")) return false;
  var gallery = document.getElementById("menu_accueil");
  var links = gallery.getElementsByTagName("a");
  for ( var i=0; i < links.length; i++) {
    links[i].onmouseover = function() {
      return showPic(this);
    }
    links[i].onmouseout = function() {
      return clearPic();
    }
    links[i].onclick = function() {
      return false;
    }
  }
}
addLoadEvent(prepareGallery);