>Hi,
>How to use this function to have BETWEEN ... AND ... comparison?
>
>Thank you

Don't. Just use >= and < .

--- If you want ALL records between 01 Apr 2009 and 15 Apr 2009
DECLARE @StartDate datetime
DECLARE @EndDate datetime
SET @StartDate = '20090401'
SET @EndDate = '20090416' -- 16 not 15


SELECT .....
FROM ....
WHERE SomeDateTimeField >= @StartDate AND
      SomeDateTimeField <  @EndDate