DECLARE@start_date DATE, @end_date DATE

SELECT@start_date = '20130103', @end_date = '20130123'

SELECTDATEPART(WEEK,Dates.Dt) AS week_nbr, MIN(Dates.Dt) AS start_date, MAX(Dates.Dt) AS end_date

FROM(

SELECTDATEADD(DAY,sv.number,@start_date) AS Dt

FROMmaster.dbo.spt_values AS sv -- You can use TALLY table instead of this

WHEREsv.type = 'P' AND sv.number <= DATEDIFF(DAY,@start_date,@end_date)

) AS Dates

GROUP BY DATEPART(WEEK,Dates.Dt)

You can find the script to generate a TALLY table below

http://www.sqlservercentral.com/scripts/Advanced+SQL/62486/