function preload(source) {  

  image_anim = new Image() ;  
 image_anim.src = source  ;
 setInterval ("checkLoad()",2000);


}

function replace_images(cible) {
    document.cible.src = image_anim.src ;

}



function checkLoad() {

  if (image_anim.complete) {
    replace_images(cible) ;
  }

}