Have you had colleagues or students send you a Word file which you can't open? Did you notice that this file ended with .docx as opposed to the usual .doc ? Well if you do have such a file, what you've got yourself there one of them newfangled Open XML files.

Office 2007 (Windows) and the yet unreleased Office 2008 (Macintosh) use a new file format called Open XML. However, Office 2008 isn't slated to ship until sometime in the second half of this year, and Open XML isn't readable by any earlier versions of Word (Windows or Macintosh). Even when Office 2008 does ship, there will be those who may not wish to upgrade. This is where the new Word 2007 Open XML file converter for Macintosh comes in handy.

Of course, you could always request of the individual who sent you the .docx file, to please resend the file as .doc (ie. they need to use the "Save as" command).