[Carnage]

you can do it without any mods.

There is a vbulletin permission on a per usergroup basis which will achieve this:

1. Create a forum
2. Goto permissions for registered users for the forum you just created
3. Under Forum viewing permissions change can view others threads to no
4. Repeat 2+3 for other usergroups you don't want to see other peoples threads (i have mine set like this for all groups that aren't admins or smods)
5. you are done.