Odd, users who belonged to a private forum in UBB.C should be added to a group in UBB.t7 which would be named something like "private_forum#".
As for adding groups:
CP -> Forums -> Group Management -> Add Group
As for adding users TO groups, this is done in member management; once you have a user profile open in the control panel, click the permissions tab; and it'll allow you to add users.
I however would like to eventually see an option in the Groups page to add users to groups vs having to edit users...
