Resize image in php

Hey!
Look at this image: picture. The images in the featured categories is in their original size. I want to set a defintive size on them, like it is in recent posts. How to do that?

The code for featured categories is:

<div id="featured-cats">
	<h3><?php _e('Featured Categories','Mimbo'); ?></h3>

		<?php
        $display_categories = get_option('openbook_cats');
        foreach ($display_categories as $category) {
        $showposts = get_option('openbook_featured_posts');
        query_posts("showposts=$showposts&cat=$category");
        ?>

<h5><a href="<?php echo get_category_link($category);?>"><?php single_cat_title(); ?>&raquo;</a></h5>

        <ul>
        <?php while (have_posts()) : the_post(); ?>
        <li class="clearfloat"></a><p class="date"><?php the_time('n/d/y'); ?> &bull; </p><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a><?php echo get_post_image (get_the_id(), '', '', '' .get_bloginfo('template_url') .'/scripts/timthumb.php?zc=1&w=40&h=40&src='); ?></li>
        <?php endwhile; ?>
        </ul>
	<?php } ?>

</div><!--END FEATURED CATS-->

I am using Mimbo the Theme Vintage Green from Darren Hoyt edited by P. Nolte