js code to change a immage
<script type="text/javascript">
function changeImage(a) {
document.getElementById("img").src=a.src;
}
</script>
<div id="main_img">
<img id="img" src="1772031_29_b.jpg">
</div>
<div id="thumb_img">
<img src='1772031_29_t.jpg' onclick='changeImage("1772031_29_b.jpg");'>
<img src='1772031_55_t.jpg' onclick='changeImage("1772031_55_b.jpg");'>
<img src='1772031_53_t.jpg' onclick='changeImage("1772031_53_b.jpg");'>
</div>