If this was *nix, then I'd say simply set the owership of the program file and the data to those of a priveleged user. The permissions on the data files can then be set so that privleged user can access them, but not standard user. Then set the setuid bit attribute for the program (so that when it is run it runs with the identity of the priveleged user who can access the data)... Of course since it's likely we're talking about Windows this isn't going to help much... ... at least not directly...

Have you considered using SQL server as the backend? In such a configuration it's possible to configure things so that user doesn't have direct access to the data (as would be the case with DBFs), but still be able to access it from within the program. Of course this generally means you'll need to make changes to your program... You could likely even use the Express edition of MS-SQL.