[Marco van Herwaarden]

I am not aware of an existing tutorial for vBulletin 4 for such a modification.

Also as i mentioned before this is not so easy to setup. A bit more techinical, but the entire setup of your forums must be identical, and stay identical. For example each user is placed in a Usergroup, linked by usergroupid. This means that both the forums must have an identical Usergroup structure with even the id's identical. The same goes for permissions. This means both boards must have the same set of permissions and both boards must have identical forums with the same forumid's. Although board-A could have forum's A & B, and board-B could have forum's A & C, but the permissions for forums A would also be shared between these boards. A lot of caveat's.

An easier, and better maintainable, solution would be to use a single install of the software with a single database, and create a modification - based on the board URL - to present it as 2 seperate forums for the users. This would also give the option to share some common forums between the boards.
(PS This would still require 2 licenses)

Yes both new users and experienced users can get help on our forums. But please be aware that vBulletin.org is a community that relies on members helping members, so no "official" support is given here.