that isn't your problem, if you aren't seeing the echo'd
in the while loop, then that is your problem, your query isn't working correctly, the results aren't coming back right, try echoing out your query before you run mysql_query, like after this
$get_posts = "select post_id, post_text, date_format(post_create_time,
'%b %e %Y at %r') as fmt_post_create_time, post_owner from
forum_posts where topic_id = $_GET[topic_id]
order by post_create_time asc";
put this
echo $get_posts;
and see if the information is coming out right, i.e make sure there is something on both sides of any = sign