You must run WordPress MU before you can use BuddyPress. Here is where you can find communities of WordPress and BuddyPress users helping one another with troubleshooting, tips, and advice:

If you are . . . The right forum for you is. . .
New to WordPress MU and need some tips and tricks on getting up and running on the platform
New to BuddyPress and want to read through advice and knowledge from other users
Experienced with WordPress MU and BuddyPress and want to interact with other developers
Looking for technical guidance on the use of BuddyPress
Looking for BuddyPress themes
Looking for BuddyPress plugins
Looking for real world examples of BuddyPress in use