Well, week, really.
Looks like my hard drive had a couple of bad sectors. TurboTax just happened to install itself onto two of them. Which locked the computer up when I tried to print my returns. Then, when I had to turn it off because it wouldn't respond for quite some time, it apparently corrupted the registry.
I've now spent the better part of two days trying to get it to work, coming to the conclusion that it will not (neither the uselessly misnamed "Startup Repair" nor restoring to an earlier point will work, though they can both tell me that, following a thorough chkdsk, the only issue is a corrupted registry, and Safe Mode won't boot up, either... so don't think I haven't tried everything that I or anyone else I've spoken to could think of), and backing up a crap-ton of files manually.
As much as I loathe Macintosh (okay, just ambivalent, really), Bill Gates and his crazy crew have essentially convinced me to jump ship. For multiple solutions to be able to tell me what's wrong but none of them (or others) to be able to fix it is ridiculous.
Looks like I'll be installing a new hard drive (just in case) and reinstalling Windows on that one just to get it to work.