Try this:
DECLARE @querydate DATETIME
SET @querydate = '2003-09-17'
SELECT DATEADD(DAY,(DATEPART(DW,@querydate))-(@@DATEFIRST)), @querydate)
If it doesn't return the proper day, do this
SELECT @@DATEFIRST
The result should be 1 if it's set to show MONDAY as the first day of the week.
-SQLBill