Try this for the product detail page:
Code:
<a href="http://pinterest.com/pin/create/button/?url={php}echo urlencode('http://www.yoururlhere.com' . $_SERVER['REQUEST_URI']);{/php}&media={$product.tmbn_url}&description={$product.producttitle}" class="pin-it-button" count-layout="horizontal">Pin It</a>
<script type="text/javascript" src="http://assets.pinterest.com/js/pinit.js"></script>