Better late than never, I guess...

DECLARE @Year    CHAR(4)

DECLARE @NextYear CHAR(4)

DECLARE @ISOWeek VARCHAR(2)

    SET @Year    = '2001'

    SET @ISOWeek = '53'

    SET @NextYear = @Year+1

SELECT

CASE

WHEN @ISOWeek > 0

 AND DATEADD(wk,DATEDIFF(wk,0,'01/04/'+@Year),0)+((@ISOWeek-1)*7)

   < DATEADD(wk,DATEDIFF(wk,0,'01/04/'+@NextYear),0)

THEN DATEADD(wk,DATEDIFF(wk,0,'01/04/'+@Year),0)+((@ISOWeek-1)*7)

ELSE 0

END AS StartDate,

       DATEADD(wk,DATEDIFF(wk,0,'01/04/'+@Year),0)+((@ISOWeek)*7)-1 AS EndDate

--todo... needs some error checking for the week number...

It returns a "0" or 01/01/1900 for the start date if the week was not found for the year...

I'm thinking that there's no ISO week 53 in 2001 but I might be using the wrong ISO "standard".