This will give the first Sunday of the given month of the given year. For the last Sunday do something similar.

DECLARE @month TINYINT

, @year SMALLINT

, @date DATETIME

SELECT @month = 8

, @year = 2003

SET @date = CAST( CAST( @month AS VARCHAR ) + '/01/' + CAST( @year AS VARCHAR ) AS DATETIME )

SELECT @date

, DATEPART ( weekday , @date )

, @date + ( 7 - DATEPART ( weekday , @date ) + 1 ) % 7