Quick code snippet to group a recordset by week. In this case we are summing hours worked per week.
SELECT DATEPART(YEAR,myDateField) AS 'Year', DATEPART(wk,myDateField) AS 'Week #', MIN(DATEADD(wk, DATEDIFF(wk,0,myDateField), 0)) AS 'Week date', SUM(COALESCE([Hours],0)) AS 'Hours' FROM myTable GROUP BY DATEPART(YEAR,myDateField),DATEPART(wk,myDateField) ORDER BY 1,2