Can Date functions be used to convert Daily Dataset to Weekly?

Dear all,

I have a dataset in the following format containing 12 years of daily data for each of the 40 district areas.  i.e. 1/1/2002 will contain 40 records for each of the 40 districts.  The example data below is for two districts only for two dates thought more of the dataset would make the question too long.

Date          District  Loss  Hectare  Count
1/01/2002   1           10    10          10
1/02/2002   2           20    20          20
2/02/2002   1           11    11          11
2/02/2002   2           21    21          21


Is it possible to use the Date function to aggregate the data to weekly?

See below output example, record 1 aggregates all values from 1/01/2002 to 7/01/2002 for the selected district area (value of district field).  The next data record aggregates all values from 8/01/2002 to 14/01/2002 for the selected district area (value of district field) and so on.

Is there a way to accompish this I haven't been able to find a solution.  

I've tried pivot tables in MS Excel but having issues with the district field, haven't been able to get the district into a column like below.  The feature to group days is great.

i.e.  
Date            District  TotalLoss  TotalHectare  TotalCount
1/01/2002    1           50            100                 150
14/01/2002  1           50            100                 150

Thanks