var currentBanner = 1;
var banners = 8;

for(var i=1;i<=banners;i++) {
  img = new Image();
  img.src = "images/banner"+i+".gif";
}

function switchBanner() {
  var el1 = $("banner1");
  var el2 = $("banner2");

  if(currentBanner == 8) {
    el1.style.backgroundImage = "url('images/banner1.jpg')";
    currentBanner = 1;
  }
  else {
    currentBanner++;

    if(currentBanner % 2 == 0) {
      el2.style.backgroundImage = "url('images/banner"+currentBanner+".jpg')";
    }
    else {
      el1.style.backgroundImage = "url('images/banner"+currentBanner+".jpg')";
    }
  }

  if(currentBanner % 2 == 0) {
    Effect.Fade("banner1");
    Effect.Appear("banner2");
  }
  else {
    Effect.Appear("banner1");
    Effect.Fade("banner2");
  }
}
setInterval("switchBanner()", 3000);