If you've got Word 2008 running and activate Witch, you'll see a window named Microsoft Word listed, even though you can't see any such window in Word 2008 itself.

It seems Word uses a hidden window for some reason, and Witch (dutiful servant that it is) sees this window and includes it in the list of available windows.

To get rid of this hidden window from the Witch panel, go to Witch's Advanced (Behavior in 3.x) tab and add Microsoft Word to the text box next labeled "Do not list windows" (or "Ignore windows with these titles" in 3.x) Poof, no more mystery window.