So Live OneCare was blocking Microsoft's update?!
I decided to see what else it was doing. Turns out it had "quarantined" the installer files I had for two VNC products because:
"This program has potentially unwanted behavior ... Remote Control Software ..."Wow. Anything to do with VNC will evidently be quarantined by OneCare. It's just too risky for regular folk to have.
I'm so glad I mostly use OS X.