Show Category Thumbails on Homepage

Hi Everyone,

I would really like to know how to show category thumbnails on the homepage. Now recent posts are shown from different categories, but I would like to replace these posts in category thumbnails / category navigation.
See http://www.fiyon.com for what I mean. So I would like to show thumbnails for cat 1, cat 2 and cat 3 instead of the posts of these categories.

My theme (Acquisto, Press75) is using a loop-gallery.php file. Could I change this file to show the wanted thumbnails? Below the content of the file;

<?php
	if (is_home()) {
		$blog_cat = get_option('of_blog_category');
		$category_id = get_cat_ID( $blog_cat );
		$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
		query_posts("cat=-$category_id&paged=$paged");
	}
?>

<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

<div id="category-<?php the_ID(); ?>" <?php post_class('gallery-item') ?>>
	<a href="<?php the_permalink() ?>" title="<?php the_title_attribute(); ?>"><img src="<?php bloginfo('template_url'); ?>/timthumb.php?src=<?php $image_one="image_one"; echo get_post_meta($post->ID, $image_one, true); ?>&h=138&w=138" alt="Product Image 1" /></a>

	<h2><a href="<?php the_permalink() ?>" title="<?php the_title_attribute(); ?>"><?php the_short_title('', '.', true, '110') ?></a></h2>
	<p>&nbsp;</p>

	<a class="price" href="<?php the_permalink() ?>" title="<?php the_title_attribute(); ?>"><?php echo get_option('of_currency_symbol'); ?><?php $get_eshop_product="price"; echo get_post_meta($post->ID, $get_eshop_product, true); ?></a>
</div> <!-- gallery-item -->

<?php endwhile; else : ?>

<div id="post-content" class="block">
	<h2 class="block-heading">Sorry, wij hebben helaas niet wat u zoekt..</h2>

	<p>What you are searching for isn't here. It is recommended that you search for something else, or click "Home" above to start from the Home Page.</p>
</div>

<?php endif; ?>

Thanks a lot!