The Good, the Bad, and the Ugly
The good: I've finally upgraded to the newest version of Movable Type, version 3.11. This means that comments are once again functional, after I disabled them months ago in response to severe levels of comment spam (and an inability on my part to get MT-Blacklist working).
The bad: It wasn't easy to get done. I couldn't get the upgrade version to install, and so I ended up having to learn a bit of MySQL -- enough to delete my database contents so that they could be rebuilt from my backup data.
The ugly: In the process of rebuilding from my backup data, all my entry URLs were changed. All of them. That means work for me to correct intra-blog links, and it means that pre-existing links from external sites into individual entries are now broken.