[troeglori]

startTimer();
function displayNextImage() {
x = (x === images.length - 1) ? 0 : x + 1;
document.getElementById("img").src = images[x];
}

function displayPreviousImage() {
x = (x <= 0) ? images.length - 1 : x - 1;
document.getElementById("img").src = images[x];
}

function startTimer() {
setInterval(displayNextImage, 3000);
}

var images = [], x = -1;
images[0] = "http://www.nordin.se/tusse.jpg";
images[1] = "http://www.nordin.se/tusse2.jpg";