Yup, it's official. The drive is corrupted. Hosed. FUBAR.
The only bright point is that my secondary drive, upon which I stored all my audio data, is still intact. So I haven't lost the recordings we did for the Consort's second CD. Everything else, though — documents, emails, 3D models, Finale scores — is toast. I've got a demo version of some data recovery software running, to see what the full version will be able to reclaim, but from the number of data sectors returning unreadable, I'm not going to get 100%. Hopefully, since the problem sectors seem to be near the beginning of the disk, it's just Windows programs that'll be unrecoverable. But I'm not counting on it.
I do have some backups, but they're not terribly recent.
I'd been meaning to get a larger hard drive, clear off some unused applications and reorganize my directory structure, but this isn't really the way I'd wanted to go about it...