Restrict a named author to one named category, can this be done?

HI guys,

I want to give access to my site for a number of named authors. I want to restrict where they can post and what pages they can manage. So for example, at least, offer them a category that is theirs to add postings to.

Is this possible? I dont see this in the current features descriptions, it just talks about roles and functions, but not restricted to specific categories.

Maybe a plugin somewhere?

Thank you