how to assign a certain theme to a certain user role?

Hello drupalers,

I have a drupal installation with several themes on it. Is there any way to assign by default a certain theme to a certain user role (after login, of course ;-))?

The second question is: Could I prevent the authenticated user, irrespective of role (except the admins, of course) to change his theme by himself?

I mean I'd like to use more than one theme but I don't want to let the user to choose among them, I want only the admin to set a certain theme for every user.

Any help is appreciated,
Gigi