en lille udvidelse til oleboles svar
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "
http://www.w3.org/TR/html4/loose.dtd"><html>
<head>
<title></title>
<script type="text/JavaScript">
function swapPic(p) {
document.getElementById("pic").src = p.href;
}
</script>
<style type="text/css">
.thumbnail {
cursor: pointer;
}
</style>
</head>
<body>
<div id="big">
<img src="et_billede.gif" id="pic">
</div>
<div id="thumbnails">
<img class="thumbnail" src="nyt_billede.gif" onclick="swapPic(this)" />
<img class="thumbnail" src="nyt_billede2.gif" onclick="swapPic(this)" />
</div>
</body>
</html>