$taxonomy = 'post_tags';  // or whatever you want

$query = NULL;
$terms = wp_get_post_terms($post->ID, $taxonomy);
if ($terms) {  
    // Get the term ids into an array for the query args
    $term_ids = array();  
    foreach($terms as $individual_term) $term_ids[] = $individual_term->term_id;  

    $args=array(  
        'post_type' => get_post_type(),
        'tax_query' => array(
            array(
                'taxonomy'  => $taxonomy,
                'field'     => 'id',
                'terms'     => $term_ids,
                'operator'  => 'IN'
            ) 
        ),
        'post__not_in' => array($post->ID),  
        'showposts' => $count, // Number of related posts that will be shown.  
        'caller_get_posts' => 1  
    );  

    $query = WP_Query($args)
}

// Place in 404.php and load subtemplate accordingly
global $wp_query, $wpdb;
if ( count($wpdb->get_results($wp_query->request)) > 0 )
    echo 'private post';

$ptype = get_post_type_object($post_type);   // eg. 'post', 'page' 

if ( !current_user_can( $ptype->cap->edit_posts ) ) { 
    wp_die( __( 'You are not allowed to create posts or drafts on this site.' ) ); 
}

$sql = sprintf( "SELECT * from {$wpdb->posts} WHERE post_title='%s' AND ( post_status <> 'trash' AND post_status <> 'inherit' AND post_status <> 'auto-draft' )", addslashes( $title ) ); 

$matching_post = get_object_vars( $wpdb->get_row($sql) );

$attachments = get_children('post_type=attachment&post_mime_type=image&post_parent='. $post_id);