wow, what an old thread
hmm, creating a new thread whenever an announcement has been created wouldn't be hard.
you've just to copy out some parts (where the first post and the thread is inserted into the db) of newthread.php and insert em into your announcement.php
for the replyingpart you have to add a field to announcementtable called threadid and fill it with the thread id of the new created thread..., then you just have to add a link to this newreply.php into the announcmentpostbit