Upgrade Complete
Well, that was more of a pain in the neck than I was anticipating, but if you're reading this, it means my Moveable Type upgrade is done.
I started off following the instructions on this page, Upgrade Path from Older Versions of Movable Type, which recommended a path of consecutive upgrades to make instead of doing it all at once. Then, I found this page, A Safe Way to Upgrade to MT 3.3 (the first step in that upgrade path). And then I got hung up on that first upgrade to 3.3. So I said, screw it, I'm going to try to jump straight to version 5.12. And here you are reading this, so it means it worked. Finally.
Anyway, I burned up all my spare time this week just getting this to work, but now I can get back to regular blogging.