exclude categories from homepage

Hi all I want to exclude three categories form my homepage, I am using the following code:

<?php get_header(); ?>

	<div id="content">

<div id="feat_section">

	<?php if (have_posts()) : ?>

<!---FEATURE LOOP STARTS--->

<?php query_posts('cat=5&showposts=1');
$ids = array();
while (have_posts()) : the_post();
$ids[] = get_the_ID(); ?>

  <div class="feat_title">

                        <div class="feat_title">
			<div class="post" id="post-<?php the_ID(); ?>">
				<h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>

                          </div>

<div class="post_author">
<p>By: <?php the_author_posts_link(); ?> | <?php the_date(); ?> | <?php the_time(); ?></p>

</div>

				<div class="entry">

<?php if( get_post_meta($post->ID, "thumb", true) ): ?>
<div class="homethumb">
<img src="<?php bloginfo('template_directory'); ?>/scripts/timthumb.php?src=<?php echo get_post_meta($post->ID, "thumb", $single = true); ?>&h=350&w=624&zc=0" alt="<?php the_title(); ?>" width="624" height="350" />
</div>
<?php else: ?>
<?php endif; ?>

				</div>

			</div>

<?php 

endwhile;
?>

</div>

</div>

<!---FEATURE LOOP END--->

<!---NEWS - LEFT COLUMN LOOP START--->

<div id="news_section">

	<div id="column_01">

<?php query_posts('showposts=15'); ?>
<?php $posts = get_posts('numberposts=15&offset=0'); foreach ($posts as $post) : start_wp(); ?>
<?php static $count2 = 0; if ($count2 == "15") { break; } else { ?>

 <div class="post" id="post-<?php the_ID(); ?>">
				<h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
				<small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>

<?php if( get_post_meta($post->ID, "homeimg", true) ): ?>
<div class=”homeimg”>
<img src="<?php bloginfo('template_directory'); ?>/scripts/timthumb.php?src=<?php echo get_post_meta($post->ID, "homeimg", $single = true); ?>&h=223&w=297&zc=0" alt="<?php the_title(); ?>" width="297" height="223" />
</div>
<?php else: ?>
<?php endif; ?>

				<div class="entry">
                                 <?php the_excerpt(); ?>
				</div>

			</div>

<?php $count2++; } ?>
<?php endforeach; ?>
</div>

<!---NEWS - LEFT COLUMN LOOP ENDS--->

<!---NEWS - RIGHT COLUMN LOOP START--->

	<div id="column_02">

<?php query_posts('showposts=15'); ?>
<?php $posts = get_posts('numberposts=15&offset=15'); foreach ($posts as $post) : start_wp(); ?>
<?php static $count3 = 0; if ($count3 == "15") { break; } else { ?>

 <div class="post" id="post-<?php the_ID(); ?>">
				<h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
				<small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>

<?php if( get_post_meta($post->ID, "homeimg", true) ): ?>
<div class=”homeimg”>
<img src="<?php bloginfo('template_directory'); ?>/scripts/timthumb.php?src=<?php echo get_post_meta($post->ID, "homeimg", $single = true); ?>&h=223&w=297&zc=0" alt="<?php the_title(); ?>" width="297" height="223" />
</div>
<?php else: ?>
<?php endif; ?>

				<div class="entry">
                                 <?php the_excerpt(); ?>
				</div>

			</div>

<?php $count3++; } ?>
<?php endforeach; ?>
</div>
</div>

<!---NEWS - RIGHT COLUMN LOOP ENDS--->

	<?php else : ?>

		<h2 class="center">Not Found</h2>
		<p class="center">Sorry, but you are looking for something that isn't here.</p>
		<?php include (TEMPLATEPATH . "/searchform.php"); ?>

	<?php endif; ?>

	</div>

<?php get_sidebar(); ?>

<?php get_footer(); ?>

I have tried adding &cat=-5,-16 to the query_posts string, but this is not working. Can anyone help.