Allow only admins to add accounts

Is there a way to only allow administrators to register new accounts. ?

Let me explain.

A non-profit organization is using punbb for a small group of persons. These people using the forums will need to apply on person at the organization for an account to access the forums.

I have already disabled the guest group ability to read the forums. But the register form is there available to them.

What they want is to once they?ve logged on to the forums as administrators, to be able to register/add new accounts to the forums.

Right know when an administrator logs in, the register button disappears. Is there a mod that would allow this behavior.

I?ll appreciate is someone can guide me in the right direction.