Needing help querying phpbb database to display on blog…

I run phpbb 2.0.21 and WP 2.0.4.

Each runs on its OWN database, they are not intergrated.

Im wanting to query the phpbb db, to show the last 5 posts topice in the sidebar of my blog. Im not sure how to queary the proper database. I know I need to define the database, but do I do this on the sidebar.php itslef?

Any help appreciated. Im so confused by all this.
Thanks