declare @dw int
set @dw = 2 -- [Sunday - Saturday] == [1 - 7]
 
declare @d datetime
set @d = '7/21/2009'

declare @first datetime
set @first = convert(varchar, datepart(mm, @d)) + '/01/' + convert(varchar,datepart(yyyy, @d))

declare @dayofweek int
set @dayofweek = DATEPART(dw,@first)

print @first + (7+(@dw - @dayofweek))%7

DECLARE @dt datetime, @date1st int
-- Save @@DATEFIRST so we can restore it later
SET @date1st = @@DATEFIRST
SET DATEFIRST 7
SET @dt = '10/12/2009'
-- Change to first of the month
SET @dt = DATEADD(d,1-DAY(@dt),@dt)
IF DATEPART(dw,@dt) <> 7
		-- If not already Saturday, add a day until it is Saturday
		WHILE DATEPART(dw, @dt) <> 7
			SET @dt = DATEADD(d,1,@dt)
PRINT CONVERT(nvarchar(30), @dt, 101)
-- Restore DATEFIRST
SET DATEFIRST @date1st

SELECT firstsaturday = DATEADD(dd,(7 - (DATEPART(dw,DATEADD(month,DATEDIFF(mm,0,getdate()),0)) + @@DATEFIRST) % 7) % 7,DATEADD(month,DATEDIFF(mm,0,getdate()),0))

SELECT firstsaturday  = DATEADD(dd,
                    (14 - @@DATEFIRST - DATEPART(dw,DATEADD(month,DATEDIFF(mm,0,somedate),0)))%7,        
                    DATEADD(month,DATEDIFF(mm,0,somedate),0))