Permissions Question

Hi, I'm sure this question has already been asked but my attempts to search for the answer didn't come up with anything so here goes. Is there a way to create a category that all users can read and post comments in existing discussions but not start a new discussion? I've written a simple blogging script that searches the forum database for all posts in the blog category and displays them on my main page. I don't want every single user to be able to blog as me though!
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