I ran Windows Update a few days ago, and it ended up installing an add in for MS Office, to allow connectivity with Office Live Workspace. Very soon afterwards, Word, Excel and Powerpoint started to crash immediately after they were started up. The Office Live add in is the culprit. I was able to open up Word in safe mode (hold down Ctrl) and deactivate the add in, after which Word started working again. After I uninstalled the add in from my computer, Excel and Powerpoint are working again.
I am not the first person to whom this happened. Hopefully my wasted time figuring this out can help save someone out there a few hours.