??
<div class="date><?php the_date();?></div>
is correct. place it where you want but keep it inside loop
<?php while(have_posts()) : the_post(); ?>
…
<?php endwhile; ?>
NEW CODE:
<body>
<!-- WRAPPER -->
<div id="wrapper">
<!-- BG WRAPPER -->
<div id="bgwrapper">
<!-- HEADER + MENU -->
<?php get_header(); ?>
<!-- CONTAINER -->
<div id="container">
<?php if(have_posts()) : ?><?php while(have_posts()) : the_post(); ?>
<div class="post" id="post-<?php the_ID(); ?>">
<div class="date><?php the_date();?></div>
<h2><?php the_title(); ?></h2>
<div class="entry">
<?php the_content(); ?>
<?php link_pages('<p><strong>Pages:</strong> ', '</p>', 'number'); ?>
<?php edit_post_link('Edit', '<p>', '</p>'); ?>
</div>
</div>
<?php endwhile; ?>
<?php else : ?>
<div class="post">
<h2><?php _e('Not Found'); ?></h2>
</div>
<?php endif; ?>
</div>
</div>
<!-- FOOTER -->
<?php get_footer(); ?>
</div>
</body>