As Ray indicated earlier, (DT_DBDATE)0 evaluates to 1899-12-30. This would be equivalent to using -2 inplace of 0 in the T-SQL calls as shown here:

/*

Date Available in db Result Expected Result

01/11/2012 01:28 03/11/2012 00:00 29/10/2012 00:00

04/11/2012 19:12 10/11/2012 00:00 03/11/2012 00:00

06/11/2012 09:34 10/11/2012 00:00 03/11/2012 00:00

12/11/2012 10:59 17/11/2012 00:00 10/11/2012 00:00

*/

WITH TestData AS (

SELECT

cast(TestDate as datetime) TestDate

FROM

(VALUES ('20121101 01:28'),('20121104 19:12'),('20121106 09:34'),('20121112 10:59'))dt(TestDate)

)

select

TestDate,

dateadd(wk,datediff(wk,0,TestDate),0),

dateadd(wk,datediff(wk,-2,TestDate),-2)

from

TestData;