Custom post query with pagination

wordpress code

<?php 
  $temp = $wp_query; 
  $wp_query = null; 
  $wp_query = new WP_Query(); 
  $wp_query->query('showposts=6&post_type=posttype&orderby=menu_order&order=ASC'.'&paged='.$paged); 
 
  while ($wp_query->have_posts()) : $wp_query->the_post(); 
?>
 
<?php
   $custom_field= get_post_meta($post->ID, 'custom_field', true);
?>
  
<h2><?php the_title(); ?></h2>
<?php the_content(); ?>
<p><?php echo $custom_field; ?></p>                           
 
 
<?php endwhile; ?>
 
<?php if (function_exists('wp_pagenavi')) { wp_pagenavi(); } else { include('navigation.php'); } ?>
 
<?php 
  $wp_query = null; 
  $wp_query = $temp;  // Reset
?>


Navigation.php code is


<div class="nav-previous"><?php next_posts_link( __( '<span class="meta-nav">&larr;</span> Older posts', 'twentyeleven' ) ); ?></div>
<div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?></div>