var bannerImg = new Array();

bannerImg[0] = "images/x.jpg";
bannerImg[1] = "images/y2.jpg";
bannerImg[2] = "images/z.jpg";

var newBanner = 0;
var totalBan  = bannerImg.length;

function wait() {
  setTimeout("cycleBan()", 4*1000);
  window.onload=cycleBan;
}

function cycleBan() {
  newBanner++;
  if (newBanner == totalBan) {
    newBanner = 0;
  }
  document.banner.src=bannerImg[newBanner];

  setTimeout("cycleBan()", 4*1000);
}

window.onload=wait;