Comment Form Outside of WP

Hello,

Is there a way to display the comment form in a directory outside of WordPress?

I want to display the form in my loop in the following file
/index.php (one dir higher then WP install)

WordPress is installed in the following directory:
/blog/

I am using the following code:

<?php require('blog/wp-blog-header.php'); ?>
<?php query_posts('showposts=3&category_name=test'); ?>
<?php while (have_posts()) : the_post(); ?>
    <a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a><br />
    <?php the_content(); ?>
    <?php comments_popup_link('no comments', '1 comment', '% comments'); ?></p>
    <?php $withcomments=true; comments_template(); ?>
<?php endwhile; ?>

But even though I am logged in I see “You must be logged in to comment.” instead of a comment form.

Thanks!