Multiple wordpress installs, one login, how to set capabilities correct?

Hi,

I put up a installation of 3 wordpress installs, bbpress and buddypress in one. They share user databases, and it works great. But now, I want users to have seperate roles on all wordpress installs, which wasn’t possible, because I got the “You do not have sufficient permissions to access this page.” error. So now I’m looking for a solution for this.

I’m using wp-wiki plugin on one of my wordpress installs, so I want to make every new user automatically a wiki-editor, but my other blogs won’t understand this role, nor can they make someone wiki-editor on registration.

So my question is, anyone got a solution for this?
Either to allow all blogs have their own roles or to let all blogs understand the roles.

Thanks,
Mitchell