Keep it simple and avoid any reference to SET DATEFIRST!

DECLARE@Year SMALLINT = 2011

;WITH cteCalendar(FirstOfMonth, LastOfMonth)

AS (

SELECTDATEADD(MONTH, 12 * @Year + number - 22801, 6) AS FirstOfMonth,

DATEADD(MONTH, 12 * @Year + number - 22800, -1) AS LastOfMonth

FROMmaster..spt_values

WHERETYPE = 'P'

AND number BETWEEN 1 AND 12

)

SELECTDATEADD(DAY, DATEDIFF(DAY, 6, FirstOfMonth) / 7 * 7, 6) AS FirstSunday,

DATEADD(DAY, DATEDIFF(DAY, 5, LastOfMonth) / 7 * 7, 5) AS LastSaturday

FROMcteCalendar