One thing, David, and I may be misunderstanding. But, you can save in .doc from Office 2007 as well as change a .docx file to a .doc file simply by renaming it.
Generally, with a paid product from Microsoft, you get two free email support sessions. Microsoft's email support is the best I have ever seen. I would run this issue by them as well. Just tell them that the install of any program causes it, so they don't pass it off on AC as the culprit.
