First off, don't use text boxes: use a Calendar control or a DateTimePicker instead. Textboxes mean that users enter what they want, which may not be a valid date (or even close to a valid date). The otehr controls only let them select "proper" dates, and save you having to validate them.
Then, just use an SQL SELECT:
SELECT * FROM MyTable WHERE MyDateColumn BETWEEN @StartDate AND @EndDate
Fill in the dates via a parametrised query, and pass the DateTime objects from the controls directly.