you don't need any plugin. You can do it in many ways, the easier one is to add the post to a category with posts that won't show, ie "privateposts".
Now open your theme's index.php and look for the loop. It can be constructed in different ways depending on the theme, but you will see something like this:
Code:
<?php query_posts ?>
Code:
<?php query_posts($query_string . '&cat=25'); ?>
where 25 is the category ID
or
Code:
<?php query_posts($query_string . 'category_name=privateposts'); ?>
of course you can exclude by many criteria, including custom fields, by author, by post ID, by date and so on, but the one above is the easier one IMHO