So Tablet-enabled versions of Windows have a feature called "Pen Flicks."
They allow you to perform certain functions in Windows by gesturing on a touch screen, either with a pen or with your fingers.
I've never really made use of the feature, personally.
That's what was killing the pressure-sensitivity in Photoshop.
I discovered this by randomly turning off any Tablet PC function I could and testing to see if it made a difference.
Oh well, at least now I know.
Munin seems to be generally hosed, though; the problem clearly wasn't with the driver for the built-in wireless adapter, as the USB one hasn't fared much better. I think I'm going to have to just do a complete reinstall.