How to protect files in Drupal

Is it possible to create an area in Drupal 6 where files can be lodged and kept secure. By that I mean accessible only by people with specific roles? We already have a list of users and each has certain roles and what we want to do is have membership lists containing names and addresses etc. so these need to be protected under the Data Protection legislation. What we need is

a) access to be given to these files for users with specific roles,
b) the ability to add and modify these same files by people with a subset of those roles and an additional role,
c) and yet be totally unobtainable or even visible to those without those roles.

Links to the file would normally be held in protected pages which we have already created.

Drupal version: