Wordpress - Don't display sub category posts

To limit the post being displayed on a category or archive page. You just need to add the following code to the top of you archive.php (or category.php) file.

$this_category = get_category(get_query_var('cat'),false);
$category_ID = $this_category->cat_ID;
query_posts( 'category__in='.$category_ID); // limit it to posts only in this category

items on the category should now only display posts that are assigned to the current category and not display any sub category items