fdImg = new Array("images/fd2.png","images/fd1.png");
thisImg = 0;
imgCt = fdImg.length;

function rotate() {
  if (document.images) {
    thisImg ++;
    if (thisImg == imgCt) {
      thisImg = 0;
    }
    document.fdTop.src=fdImg[thisImg];
    setTimeout("rotate()", 2*1000);
  }
}