You could set up a summary report that groups your customer data by month. You can set up your layout so that each Month's data starts a new page. Then you could print out the most recent two months of data and place the pages side by side.
You might also set up two large filtered portals where each portal filters your data by a different month.
You can also open two windows and display the current month's data in one window and the previous month's data in a second window so that you can place them side by side on your screen.