Pivot Tables in Excel are useful for comparing 1 report to another, I have a low level of experience and it took a lot of trial and error but I use it to compare previous paydex scores with the new scores. Copy (don't cut from your original)each report into 1 Excel file onto different pages, add a few extra sheets. IF the column amount is a number in text format and you need to calculate the values like a number, you will have to copy it and Paste Special (Value, Add) it into another column before you start to make the pivot table. Label the Columns that you want to "compare" with different names (ie Jun 2010 and the other July 2010) so you can distinguish them. You may also want to delete any columns you don't care about before you start the Pivot.
When you are ready choose Data, Pivot Table, Multiple Consolidation Ranges, Pivot Table, Next, Create a single page for me, Next. This will bring you to Range, then you can copy the range on 1 sheet, then choose Add, copy the range on 2nd sheet, then Add, choose Next. Click on a blank sheet and go to cell A1, choose Layout. Then double click on Count of Value, then choose Sum, OK, Finish.
You get a combined sheet and you may want to hide (can't delete them now) any columns you don't need to look at. From there you can do some conditional formating to make it subtract one column from another and bold/change font color/change background color etc to help you focus on the data you actually need to see. I would suggest making some smaller tables and playing with them until you get a bit morecomfortable with it BEFORE trying to tackle a big project otherwise it can be frustrating to have to keep starting over.