As the title of this thread says MC returns a critical error # 30, then closes. Some suggested that that error happens when MC's .exe is changed, which is exactly what the W32pate.b virus does. As for other clues, there weren't many and actuallly I haven't been using the disinfected machine long enough to say minor glitches I saw were the result of the virus. Many I just chalked up to Windows being Windows, the imperfect OS that it is. I'll know better in a few weeks. One I strongly suspect though, is that most times I closed Windows, I would find one or two hung copies of Windows Explorer in the background, which had to be closed manually before shutdown. Though that would have shown up in Task Manager the 2nd or 3rd WExplorer functioned normally and transparently.
Thanks to eveyone who made suggestions. I was already planning for life without Media Center, and that's not a good thing.