All can view but only specific usergroup can post

[Cyn]

I want to restrict the posting to a specific forum so that only a specified usergroup can post there yet all other usergroups have read-only access. Of course the moderator of the forum should be able to access and fulfill necessary moderator duties.

This by Logician worked great in restricting posting based on number of posts. But in this case the number of posts is not important. It's the usergroup that qualifies posting privileges that I need now.

Thanks!

Edited to add: I wonder if I could use the hack above by simply leaving out the line qualifying by post counts???