Sorting with materialized paths

My apologies. This isn't PG-specific, but since this is running on PostgreSQL 8.4, maybe there are specific features which might help.

I have a tree structure in a table and it uses materialized paths to allow me to find children quickly. However, I also need to sort the results depth-first, as one would expect with threaded forum replies.

id | parent_id | matpath | created
----+-----------+---------+----------------------------
2 | 1 | 1 | 2010-05-08 15:18:37.987544
3 | 1 | 1 | 2010-05-08 17:38:14.125377
4 | 1 | 1 | 2010-05-08 17:38:57.26743
5 | 1 | 1 | 2010-05-08 17:43:28.211708
7 | 1 | 1 | 2010-05-08 18:18:11.849735
6 | 2 | 1.2 | 2010-05-08 17:50:43.288759
9 | 5 | 1.5 | 2010-05-09 14:02:43.818646
8 | 6 | 1.2.6 | 2010-05-09 14:01:17.632695

So the final results should actually be sorted like this:

id | parent_id | matpath | created
----+-----------+---------+----------------------------
2 | 1 | 1 | 2010-05-08 15:18:37.987544
6 | 2 | 1.2 | 2010-05-08 17:50:43.288759
8 | 6 | 1.2.6 | 2010-05-09 14:01:17.632695
3 | 1 | 1 | 2010-05-08 17:38:14.125377
4 | 1 | 1 | 2010-05-08 17:38:57.26743
5 | 1 | 1 | 2010-05-08 17:43:28.211708
9 | 5 | 1.5 | 2010-05-09 14:02:43.818646
7 | 1 | 1 | 2010-05-08 18:18:11.849735

Rationale: this is for a threaded forum and id 6 is a reply to id 2, so it needs to show up after that one. Here's the rough structure of what the output would look like (imagine an HTML forum):

* id 1 (root post)
* id 2
* id 6
* id 8
* id 3
* id 4
* id 5
* id 9
* id 7

How would I work that out? Can I do that in straight SQL or should additional information be added to this table?

Cheers,
Ovid
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