A lot of people set up a Calendar table specifically for this kind of thing -

see http://www.sqlservercentral.com/scripts/Date/68389/ for example.

Using this as a base, I came up with this:

DECLARE @StartDate Date,

@EndDate Date,

@WeekStart TinyInt;

SELECT @StartDate = '03 Jan 2013',

@EndDate = '23 Jan 2013',

@WeekStart = 1;

WITH cte_date_base_table AS

(

SELECT

@StartDate AS calendar_date

UNION ALL

SELECT

DATEADD (DAY, 1, CTE.calendar_date)

FROM

cte_date_base_table CTE

WHERE

DATEADD (DAY, 1, CTE.calendar_date) <= @EndDate

)

, cte2 AS

(

SELECT calendar_date,

DATEPART(dw, calendar_date) AS dow,

DATEPART(week, calendar_date) AS week_nbr

FROM cte_date_base_table

)

SELECT week_nbr,

MIN(calendar_date) as start_date,

MAX(calendar_date) as end_date

FROM cte2

GROUP BY week_nbr