BuddyPress.org

Maybe you should try this solution: works for wp3.1 multisite, also there are hints when working with single-site. I have it working on my multisite (but with the old code example).
The first link shows you how to make a selection for roles at signup: http://cleverness.org/2011/01/27/updated-buddypress-user-roles-code/
The second link is for the setup of which profilegroups (fieldgroups) are shown on certain roles: http://cleverness.org/2010/10/13/user-types-in-buddypress-assign-xprofile-groups/

Give it a try, it works for me.