segue o codigo:
javascript:
function changeImg(foto) { if(document.full.src != foto){ document.full.src = foto; } }
html:
<div id="full"><img name="full" src='img/Rubens 001.jpg' alt="" height="300" width="500"/></div> <div class="mini"> <a href="#" target="_self" title="" onclick="changeImg('img/Rubens 001.jpg')"><img src="thumbnails/Rubens 001.jpg" /></a> <a href="#" target="_self" title="" onclick="changeImg('img/Rubens 002.jpg')"><img src="thumbnails/Rubens 002.jpg" /></a> </div>