Roles and permissions

I'm completely new to Moodle but having looked through the documentation I can't seem to find a way of setting Moodle up to do the following:

Once a user has logged in I want to display on their frontpage a list of categories & courses depending on who they are (not depending on which courses they are enrolled in). We'll be using LDAP authentication so if the user is in a certain group in LDAP how can I ensure that he/she will only see a list of categories / courses that the group in LDAP gives them permission to see?

Not sure if this post should be under the user authentication forum or here as it might depend on roles?

Any help would be appreciated.

Cheers, Chris