Per the documentation:
<script type="text/javascript" charset="utf-8">
$(document).ready(function(){
$("a[rel^='prettyPhoto']").prettyPhoto();
});
</script>
Source: http://www.no-margin-for-errors.com/projects/prettyphoto-jquery-lightbox-clone/prettyphoto-faqs/
You will also need to import the standard jQuery library to use jQuery plugins!