However, when the missus tries to open certain file types, like Docx and RTF, up pops Office 2007--the trial for which has long since expired. Why don't these files open in Symphony instead?
For whatever reason, certain file types remain "associated" with Office, meaning Windows doesn't know it's supposed to direct them to Symphony. Fortunately, that's an easy thing to fix.
In Vista and Windows 7, you can click Start, type Default, and then hit Enter to load Windows' Default Programs menu. You can then click Associate a file type or protocol with a program, choose the file type in question, click Change Program, and go from there.
Whew! That's a lengthy process. My preference is simply to right-click any file that's incorrectly associated (like, say, one of the aformentioned RTFs), mouse over Open With, and then click Choose Default Program.
If the program you want appears under Recommended Programs (and it should), click it, and then make sure the checkbox for Always use the selected program to open this kind of file is checked. Click OK and you're done. From this point on, any attempt to open that file type (not just that file) will result in Windows loading the selected program.
If the program doesn't appear, you can click Browse to locate its executable on your hard drive. That's not the easiest task in the world, but you'll need to do it if you want to re-associate that file type.
I should add that the most common file-association hassle you're likely to face is with media files: MP3s, videos, and the like not opening where you want them to. This solution works with those kinds of files as well as documents.