Exclude Categories From Archive?

Hey Everyone,

Below is the code on my archive.php file and what I am looking for is how to edit the code to exclude some categories from the archive as I dont need all the categories in the archive.

All help appreciated,

Thanks

<?php
/**
 * @package WordPress
 * @subpackage A Step Above
 */

get_header(); ?>

<div id="subnav">
<?php do_action('wp_menubar','subtalk'); ?>
<!-- subnav --></div>

<div id="content">

<div class="three-col">

			<?php /* If this is a category archive */ if (is_category()) { ?>
			<h2 class="archive_head">Entries Tagged as '<?php echo single_cat_title(); ?>'</h2>
			<?php /* If this is a tag archive */ } elseif (is_tag()) { ?>
			<h2 class="archive_head">Entries Tagged as '<?php echo single_tag_title() ?>'</h2>
			<?php /* If this is a date archive */ } elseif (is_date()) { ?>
			<h2 class="archive_head">Entries from <?php the_time('F Y'); ?></h2>
			<?php /* If this is a monthly archive */ } elseif (is_month()) { ?>
			<h2 class="archive_head">Entries from <?php the_time('F Y'); ?></h2>
			<?php /* If this is a yearly archive */ } elseif (is_year()) { ?>
			<h2 class="archive_head">Entries from <?php the_time('Y'); ?></h2>
			<?php /* If this is a search */ } elseif (is_search()) { ?>
			<h2 class="archive_head">Search Results</h2>
			<?php } ?>

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

			<div id="post-<?php the_ID(); ?>"  <?php post_class(); ?>>

				<div class="post_content">
				<h2 class="entry-title"><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h2>
				<div class="entry clearfix">
					<?php the_excerpt(); ?>
				</div>
				</div>
				<span class="clear"></span>
				<div class="post_meta rounded">Posted by <a href="#"><?php the_author(); ?></a> in <?php the_category('/'); ?> / <?php comments_popup_link('No Comments.', '1 Comment', '% Comments'); ?> </div>

			</div><?php /* end post */ ?>
			<?php endwhile; ?>
		<?php else : ?>
			<h2 class="page_header center">Not Found</h2>
			<div class="entry">
				<p>Sorry, but you are looking for something that isn't here.</p>
				<?php get_search_form(); ?>
			</div>

		<?php endif; ?>

</div><!-- #content -->

<?php get_sidebar(); ?>

<!-- content --></div>

<!-- wrapper --></div>

<?php get_footer(); ?>