previous_posts_link not showing previous posts

Hi all,
I have a strange problem with next_posts_link and previous_posts_link. I created a custom post type and a simple archive page for it: no problems, everything works fine. But when I add next_posts_link and previous_posts_link they point only at the latest post (not showing the older ones).
I googled and it seems to be a $paged variables problems and I tried to cut-paste code I found on the net (not the proper method, I know…) without results…

Here is the code of my page archive for the type post “demandes”:

<?php /* Template Name: Demandes Type Archive */ ?>

<?php get_header(); ?>

<div id="content-container">
 <div id="content" role="main">

<?php

        global $query_string;
        query_posts("post_type=demandes&post_status=publish&posts_per_page=2");
        if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

<h2><a>" title="<?php the_title(); ?>"><?php the_title(); ?></a></h2>
<?php the_excerpt(); ?>

<?php endwhile; endif; ?>
<div class="navigation">
<div class="alignleft"><?php next_posts_link('More ?'); ?></div>
<div class="alignright"><?php previous_posts_link('? Previous'); ?></div>
</div>
<?php wp_reset_query(); ?>

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

<?php get_sidebar();?>
<?php get_footer();?>

Thanks for your help