I have setup a custom page template to show a archive of my

I have setup a custom page template to show a archive of my blog posts. The issue I am having is the pagination works but it displays the exact same blog posts on each page.

<?php
$temp = $wp_query;
$wp_query = null;
$wp_query = new WP_Query();
$wp_query->query('showposts=18&post_type=post&offset=9'.'&paged='.$paged);

if ($wp_query->have_posts()) : while ($wp_query->have_posts()) : $wp_query->the_post(); ?>

Loop Stuff Here

<?php endwhile; ?>
<div class="nav-previous">
<?php next_posts_link( 'Older posts' ); ?>
</div>
<div class="nav-next">
<?php previous_posts_link( 'Newer posts' ); ?>
</div>
<?php endif; ?>