bbPress.org

OK, so davidbaldwin opens a can of worms with his advice here.

I don’t recommend doing it this way, my advice is to create two separate themes for WordPress and bbPress that look alike and if you enable “deep” integration, then carefully pick the functions you want to use from WordPress and insert them into the bbPress template.

Throwing in the whole WordPress header is potentially problematic. It’s possible to do it cleanly with a lot of work, but most people won’t have the knowledge or the time to do that.