Selecting date range from form

[Dom.]

Hello All,

I Have a query with a date range which is entered
from a form called frmDtRange. I would like the user to
have the option to enter a specific date range or just
enter nothing and get all dates instead of just no
records. How do I do this ? So far I have:

==========================
Between [forms]![frmDtRange]![txtBPFrom] And
[forms]![frmDtRange]![txtBPTo]
==========================

Also, is there a way to change the criteria of a query
from a form ? If so how ? Please write a sample code.
I want the user to be able to either choose a date range,
a year, or a month and a year from the form.

Thanks in advance to all.
Dom.