I have a blog with Admin level, Author level and Contributor level users. Users in all three levels can post, but I only want them to be able to post in certain categories. For example, I want Admins to be able to post in all categories, Authors to be able to post in just the 'Music', 'Videos', 'Films' and 'Blogs' categories, and Contributors to be able to post in just the 'Blogs' category.
The problem is that users on all three levels are presented with the same list of categories when they add a new post. Is there something I can do to hide certain categories from the 'Add new post' page for certain user levels to prevent them from posting in the categories they're not allowed to? I've tried searching for plugins to do the job, but I've not found the right one. Does anybody know of one?