hack: writing posts to extra database table

I am starting out trying to get wordpress post to generate a bbPress forum (not forum topic)

Assuming that:
there are few locations where wordpress actually writes to the posts database

I want to add simple code to write selected and appropriate info to the relevant bb table (they share a database).

Ignoring any complications at the bb end, for the time being, I was first wondering if anyone could point me to where the code is that actually inserts the post data into the mysql table?

And any other quick hints that might help. I am quite new to all this but want to learn fast.

thanks!