Read Only Forums

Does anyone know a way to make certain forums or forum groups read only?

I want to use forums as a secondary purpose of posting information for members to read, but I dont want to take away members' ability to post in forums altogether.  So I need a way to make specific forums as 'read only'. All I can find is I can make it Public or Private, but private locks users out of reading as well as writing.

Any ideas?

Thanks.

Let me now what you come up with as I would like this also.  Better yet, a way to give certain membership levels access to certain forums.  Right now it is "all or nothing" - members can either see all private forums or none.

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Rob