Double post listing on page

Hello
I am using exec-PHP so I’m putting some code directly on the page.

The problem is that when I put the query_posts of a category on my page, it queris it two times!

what chould i do?

This is teh code on the page.php file

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

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

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

and the part of code on the page:

<?php query_posts('cat=12&showposts=5'); ?>
<?php while (have_posts()) : the_post(); ?>
<li><a href="<?php the_permalink(); ?>">
          <?php the_title(); ?></a></li>
      <?php endwhile; ?>

Thank you