If you are talking about the Access Application windows, I don't think you
can since they are parts of the Windows "standard" interface. (There may be
ways using the Win API but I don't know). The best you can do is to make
the Application Close button (X) ineffective.
However, like Marsh wrote, users expect it to behave the same as other
applications and if you prevent users from using the Close button like other
applications, they may unplug the power and corrupt the database.
It is much better to allow the users to use the Close button and simply use
code to do whatever you need to do before closing down.
HTH
Van T. Dinh
MVP (Access)