[_ck_]

You will need bbPress 1.0 to integrate with wpmu 2.6 (or even wp 2.6) which is only available via the trunk. It’s also not stable yet, so not recommended for live sites.

Sam has mentioned possibly doing some kind of early 1.0 alpha release soon to help/please some people who insist on using 2.6 but I don’t know the specifics of the timetable he has in mind.