If you’re using Windows 7 there may be a whole host of features you’re not taking advantage of. One of those is the ability to snap windows to the side of the screen.
To do that, drag an open window, say, for Word, to the side of the screen. You’ll find it snaps into place and then takes up half the screen. You can do the opposite with another window to compare the two side by side.
You may not use feature often, but it’s a good way to compare documents such as spreadsheets.