I want posts accessible but don't want anybody to be able to login or make any new posts.

I thought closing it would do that but you can't access it all when closed.

You can set the group permissions to read only. If you like you can set the gropu guest and user to read only. So no one except Admins and Mods can post.

Is there a way to also disable logins execpt the admin?

If you close the board only the admin can login.

The only way to block logins would be to close the forum, but then people couldn't browse. you could try editing out the login link from the header.tpl file.

As for browsing, adjusting it so groups have no posting ability would do this.