bbPress.org

If you’re able to tweak a regular template to a wordpress theme than is the next step to bbpress not so far.

I embedded both applications into my own site:

http://www.finalwebsites.com/forums/

http://www.finalwebsites.nl/blog/

my advice start with the header and footer!

surround anything with one div container, open that container in the header and close it inside the footer