need help with timthumb.php

Hi,

This is the link

this is my code to show a nivo slideshow.

<?php
	$tmp = $wp_query;
	$wp_query = new WP_Query('posts_per_page=10&category_name=referenties');
	if(have_posts()) : while(have_posts()) : the_post(); ?>
          <a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_post_thumbnail('featured-thumbnail'); ?></a>
	<?php endwhile;
endif; ?>

I need the featured image to resize with the timthumb.php script. This is what I need (I think):

timthumb.php?src=the_post_thumbnail('featured-thumbnail');&h=320&w=450

Where should I add this code? Thanks in advance!