Sorry for asking a question that you had already answered.

I use Office2003 but have not installed the converter package because it requires certain upgrades that I do not want to install. But it seems to me that even though you have the converter package installed, your opsys does not know what appl to use for .docx file unless you tell it each time. Have you explicitly set Word as the program to be used with .docx files? Have you checked to see if Word is the appl associated with .docx files? That can easily be done using Windows Explorer: Tools | Folders | File Types

Whenever I encounter a new file type and figure out what appl should be used to open it, I explicitly set up that relationship (as above) so I never have to go through the selection process again.