Thanks ted. I'll update my backup (so I can roll back to working version if I need to) and go hunt down those files.
I don't think I'll need to overwrite HTCProvisionDrv, the current version seems to work just fine. In fact, if it doesn't, there won't be any way to do the overwrite. It's just the registry and filesystem drivers that were broken.
Now I'm wondering what the other HTC drivers do. There's a specific one for Connection Setup and for HTC YouTube, plus drivers for "HTCBgService" (a way to run tasks in the background, I assume) and "HTCVersionUtility" (probably not useful, but maybe?). It would be interesting to examine the APIs of those.
For that matter, it would be interesting to examine the API of things like the provision driver. It appears to have full permissions, but the DMXMLCOM.DLL library used to interface with it has a fairly limited API (no way to get the result of a provxml query, for example). Talking directly to the driver may work better.
Anyhow, off to find the correct CAB!