Just to follow up on Jon's point here: the constraint he is talking about is not with persons. The organizations you enter into the system are entered as *parties*, which is a completely different thing.
By entering them as parties, you're using the standard OpenACS way of entering organizations like this, and other packages can take advantage of the organizations you've entered.
I haven't looked thoroughly into the parties data model, but I believe this is the best way to do things.
