WordPress Show the excerpt from all posts

I have archives.php to show excerpts from the posts. (this is what I need http://www.m2advocaten.nl/nieuws (on the left))

 <!-- Start the Loop. -->
 <?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

 <!-- Test if the current post is in category 3. -->
 <!-- If it is, the div box is given the CSS class "post-cat-three". -->
 <!-- Otherwise, the div box is given the CSS class "post". -->
 <?php if ( in_category('3') ) { ?>
           <div class="post-cat-three">
 <?php } else { ?>
           <div class="post">
 <?php } ?>

 <!-- Display the Title as a link to the Post's permalink. -->
 <h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>

 <!-- Display the date (November 16th, 2009 format) and a link to other posts by this posts author. -->
 <small><?php the_time('F jS, Y') ?> by <?php the_author_posts_link() ?></small>

 <!-- Display the Post's Content in a div box. -->
 <div class="entry">
   <?php the_excerpt(); ?>
 </div>

 <!-- Display a comma separated list of the Post's Categories. -->
 <p class="postmetadata">Posted in <?php the_category(', '); ?></p>
 </div> <!-- closes the first div box -->

 <!-- Stop The Loop (but note the "else:" - see next line). -->
 <?php endwhile; else: ?>

 <!-- The very first "if" tested to see if there were any Posts to -->
 <!-- display.  This "else" part tells what do if there weren't any. -->
 <p>Sorry, no posts matched your criteria.</p>

 <!-- REALLY stop The Loop. -->
 <?php endif; ?>

The problem is that it’s not showing the posts, but rather the page content (with this code)
And I need just a page that shows the posts.
Do I need to add a function or something?

I have tried page of posts also but it didn’t work.