Usually MS Word or any other MS Office application crashes, it is due to a loaded add-in that wants to make your life “happier”.
When MS Word 2007 begins to crash erratically, but most probably upon closing down or showing that the crash happened in mso.dll,
do the following:

Open the Registry Editor (regedit.exe)
Go to HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Word\Data
Delete it with [...]