Arrange All Windows Vertically
Use at your own risk; see the Script Caveat
In Word, Window>Arrange All arranges the windows horizontally, stacked on top of each other. J.E. McGimpsey had written a great macro to arrange the windows vertically instead, but macros do not work in Word 2008.
Shawn Larson of the MacBU has translated the macro into AppleScript. You can download it here.
Save the script in [username]/Documents/Microsoft User Data/Word Script Menu Items to make it appear in the Word Script Menu.
You can assign a keyboard shortcut to the script.
The script will automatically adjust for the Dock. But by design, the script leaves some space at the bottom and right of the documents. You can change how much space is left by opening up the script and editing a couple of lines—see the comments in the script itself.
There is no special handing in the script for multiple monitors, and it has not been tested with that configuration.