Comparing multiple all having the same data structure

HI everyone,

I have been working on a data comparison project for a while now.  I finally have my data in Access, however I need a little push in the right direction.

My scenario is:
I have a company which provides me a 52 week forecast every month.
I have imported the forecast for each month into Access.
My tables are all identicle. [ID], [PN] Part Nr, [Date], [FQ] Forecast Quantity.

I need to find a way to compare any two ore more tables to find the changes in the forecast qty for the same PN and Date period.

an example
January table
PN 12345, 6/1/2011, 25
PN 12345, 7/1/2011, 150
PN 12345, 8/1/2011, 93

February table
PN 12345, 6/1/2011, 25
PN 12345, 7/1/2011, 230
PN 12345, 8/1/2011, 125

March table
PN 12345, 6/1/2011, 55
PN 12345, 7/1/2011, 230
PN 12345, 8/1/2011, 0

I'd want to know how the forecast numbers changed for each part number in the same period broken down by the monthly import table.

Each table has 496 PNs, is actually broken into 52 Date ranges with a forecast value for each so I have 25,792 individual records to move thorugh per table.

I appreciate any guidence that can be given.  

MC