The Windows logon name can be obtained by:

Environ("UserName")

which works everywhere (queries, forms, reports, macros, VB code...). The
suggestions below assume that users only access data through forms, reports
etc, without opening the tables directly. To ensure they cannot do the
latter, you will need some VB code to disable the startup bypass key (Shift)
and Show database window key (F11) on your front end. They will still work
without this precaution, but a knowledgable user will be able to gain access
to the tables.

In order to restrict user access to a table's records (at record level), you
need to include a field in the table to store clearence information, such as
the user logon name itself, or a department ID, and make the recordsoyurce
of the form(s) though which the table is accessed a query that filters on
it; if the field stores the user logon name itself then it's just a question
of filtering on the current user's logon name; if it's a department or
workgroup or something, you need a table associating users with departments
(etc), and a DLookup in the filter to get the department based on the user's
network logon name.

In order to provide or deny user access to forms etc. depending on their
logon, you can use some simple VB code in the On Open event (or wherever
applicable) of your swhitchboard (or other form) which enables or disables
the command button(s) opening the forms; this requires a table to hold the
information on what is permitted for each user.

HTH,
Nikos