2 domains, 2 licences but some shared forums

[Bloory]

I've got two brands each with vbulletin installed. For some things, like announcents and general chat type forums I'd like to double up but for some brand-specific sections I'd like to restrict viewing to the appropriate domain.

I understand that this might well be possible, certainly seperate skins are. I have two licences but how would I go about achieving this please?

I can see that forum permissions for members would be the answer. What about guests?

I'm not too bothered if there was a chink in the merge so long as it was not confusing.

Thanks in advance for any help you can give,

Jon