I'm trying to run an update statement that'll get the smallest value
from one table and insert it into another.  The following update
statement does this (I think), but doesn't work on any version of MySQL
that I have access to (4.0 and 3.23):

UPDATE phpbb_users SET (user_firstpost) = SELECT MIN(post_time) FROM
phpbb_posts WHERE phpbb_posts.poster_id = phpbb_users.user_id;

I think the reason it doesn't work is because it uses a subquery, as
well.

The following update - which does work in 4.0 unlike the previous one -
seems to do the same thing:

UPDATE phpbb_users AS u, phpbb_posts AS p1
  LEFT OUTER JOIN
  phpbb_posts AS p2
  ON p1.poster_id = p2.poster_id AND
     p2.post_time < p1.post_time
  INNER JOIN
  phpbb_posts AS p3
  ON p3.post_time = p1.post_time
SET u.user_firstpost=p3.post_time
WHERE p2.post_time IS NULL AND
  p1.poster_id = u.user_id;

Unfortunately, this update doesn't work in MySQL 3.23.  When I try to
run it, I get the following error:

You have an error in your SQL syntax near 'AS u, posts AS p1 LEFT OUTER
JOIN posts AS p2 ON p1.poster_id = p2.p' at line 1

So..  any ideas as to what's wrong with the second update?
Alternatively, any ideas as to how to do the first update in a way that
works with MySQL 3.23?