BuddyPress Restrict Group Creation plugin by nuprn1, will restrict creating groups and group settings to certain WP Capabilities and various member thresholds (forum posts, friends, status updates, days since registered, achievements)
In addition, this plugin will auto-demote the group creator to group mod to ensure group settings may not be modified after creation. You may also define a group admin and mod that will be auto-assigned to all new groups. (requires adding 2 config lines)
Plugin homepage: http://blog.etiviti.com/2010/03/buddypress-restrict-group-creation/