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 http://mu.wordpress.org/forums
New to BuddyPress and want to read through advice and knowledge from other users http://buddypress.org/forums
Experienced with WordPress MU and BuddyPress and want to interact with other developers http://buddypress.org/developers
Looking for technical guidance on the use of BuddyPress http://codex.buddypress.org
Looking for BuddyPress themes http://buddypress.org/extend/themes
Looking for BuddyPress plugins http://buddypress.org/extend/plugins
Looking for real world examples of BuddyPress in use http://wordpress.org/showcase/flavor/buddypress