Mac OS X 10.7.2 and Microsoft Word 2011

I recently installed Microsoft Office 2011 on the Mac Computers in my classroom.

When my students open up the Microsoft Word Application and open a new Document, the software is still opening up the document in Word 97-2004 (.doc) format. I want them to be saving in (.docx) format.

I went to Word>Preferences>Save and the "Save Word Files as:" setting is set to Word 97-2004 (.doc). I Change it to Word Document (.docx), but when they close the application, and open it up again, the setting is reset back to Word 97-2004 (.doc).

Is there another setting somewhere in the OS X Settings, or buried in the Word Settings, that is forcing New Documents to open up in Word 97-2004 (.doc) format instead of Word Document (.docx)?

Thank You,
Matt Durchik
Business Education Instructor
Fivay High School
(E-Mail Removed)

Oh, yikes. I was just wondering if I could install Office:Mac 2011 on my machine which has been running Office:Mac 2004 since, well, actually 2003. Oh, geez. And I have at least a gazillion Word documents.