thanks mate!!
i got it to work from:
SELECT pt.privmsgs_text_id, u1.username as from_user, u2.username as to_user, pt.privmsgs_text
FROM phpbb_privmsgs_text pt, phpbb_privmsgs p, phpbb_users u1, phpbb_users u2
WHERE pt.privmsgs_text_id = p.privmsgs_id AND p.privmsgs_from_userid = u1.user_id...