I found the same problem. When the first of the month is the day in question, it returns the second week. I modified it to this.

DECLARE @DATE DATETIME,@GETDATE DATETIME,@MONTHSTDATE DATETIME,@STARTDATE DATETIME

SET DATEFIRST 6

SET @STARTDATE='06/21/2010'

SELECT @MONTHSTDATE = CONVERT(DATETIME, CONVERT(VARCHAR(5),DATEPART(MM, @STARTDATE)) + '/01/' + CONVERT(VARCHAR(5),DATEPART(YYYY, @STARTDATE)) +' ' + '00:00:00 AM')

PRINT @MONTHSTDATE

PRINT DATEPART(DW,@MONTHSTDATE)

SET @getdate-2=@MONTHSTDATE - CASE WHEN DATEPART(DW,@MONTHSTDATE) = 1 THEN 0

ELSE (DATEPART(DW,@MONTHSTDATE)-8)

END

PRINT @getdate-2