Assuming that the work week is Monday to Sunday here is how you can do it.
Declare @date1 datetime
set @date1 ='9/3/2006'
SET DATEFIRST 1
select @date1 as date1,DateAdd(d,-1 * DatePart(dw,@date1)+1,@date1) as WeekBegin
SET DATEFIRST 7
Changing any date will get you to the Monday of the week. You can use this logic on the date columns to get what you want.
Hope this helps
Thanks
Sreejith