In case anyone is wondering, this is how it stands right now:

I spend about an hour or two in an online support session with a Microsoft
support dude named Abilash. Nice guy. He eventually started an Easy Assist
connection to my computer. After verifying that everything I was saying was
true, he suggested a clean hardware and software boot. I tried this the best
I could (starting up in diagnostic mode?) and it didn't fix the problem. I
couldn't give him my cell phone number at the moment, so he marked closed it
as "Not Resolved." I'm going to call tomorrow to reopen the case, because
his steps did not work. After looking at my Device Manager, he said that he
thought he had seen this problem before, and it was the result of corrupt
network drivers. However, I disabled, uninstalled, and reinstalled the
official Microsoft drivers that come with Vista, and this did not fix the
problem either.