Loop posts between from current post date and a set date?

I’m trying to make a loop that displays 5 posts between two dates. This shouldn’t be hard but one of the dates is the date of the current post and is therefore a variable…

This is what I’ve come up with but it doesn’t work. No errors but just shows all posts.

function filter_where($where = '') {
        $where .= ' AND post_date >= "2000-01-01" AND post_date <= "' . $date .'"';
    return $where;
  }
add_filter('posts_where', 'filter_where');
query_posts('showposts=5');

The $date is retrieved from another loop like this:
$date = the_date('Y-m-d');

and I’ve tried to define $date manually but it won’t work:
$date = "2010-01-01";

Would be grateful for any ideas!