Open up viewtopic.php and go to line 213. Replace:
$result = $db->query('SELECT u.email, u.title, u.url, u.location, u.use_avatar, u.signature, u.email_setting, u.num_posts, u.status, u.registered, u.admin_note, p.id, p.poster, p.poster_id, p.poster_ip, p.poster_email, p.message, p.smilies, p.posted, p.edited, p.edited_by FROM '.$db->prefix.'posts AS p INNER JOIN '.$db->prefix.'users AS u ON u.id=p.poster_id WHERE p.topic_id='.$id.' ORDER BY p.id LIMIT '.$start_from.','.$disp_posts) or error('Unable to fetch post info', __FILE__, __LINE__, $db->error());
with
$result = $db->query('SELECT u.email, u.title, u.url, u.location, u.use_avatar, u.signature, u.email_setting, u.num_posts, u.status, u.registered, u.admin_note, p.id, p.poster, p.poster_id, p.poster_ip, p.poster_email, p.message, p.smilies, p.posted, p.edited, p.edited_by FROM '.$db->prefix.'posts AS p INNER JOIN '.$db->prefix.'users AS u ON u.id=p.poster_id WHERE p.topic_id='.$id.' ORDER BY p.id LIMIT '.$start_from.','.$disp_posts.' DESC') or error('Unable to fetch post info', __FILE__, __LINE__, $db->error());
"Programming is like sex: one mistake and you have to support it for the rest of your life."