Set usergroup based on a link to a forum?

[PeteW]

Hiya,

We have a site with two distinct types of users who have logins to separate areas of the site. I'd like them to be able to register in separate usergroups of a vBulletin forum, so that they both have a link to the forum within their own part of the site, and the forum would automatically know which usergroup to put them in based on where they came from.

Would this be possible at all? Perhaps using a session variable or a variable in the querystring of the link to the forum?

Cheers

Pete