That's UShop.
And he prolly did the crews through the vb3.0's default system for public joinable usergroups.
Just create a new usergroup and where it asks if it's publically joinable, click yes. After that you can set who is the "Group Leader" they are the one that approves new members.
If you click the other box right below public joinable, that says something like, permissions can override. Then you can setup forums for just that clan and give only that new group access to it.
In the postbit, that'd be easy, it'd just be something like
Code:
Crew: <if condition="is_member_of($post, 63)">Such and Such group</if><if condition="is_member_of($post, 64)">Such and Such Other group</if>
Etc.
I've done something similar to all this on my site at
www.mmogcommunities.com even used vba cmps to give each clan their own homepages like
www.mpsquad.net and
www.mmogcommunities.com/index.php?page=gofac1