OK, so it's not so much a "solution" to a problem - as it is just a sidestepping of the issue... but I bought a new video card. Problem gone.
However that does lead me to two theories... a) The video card really was the issue and I have actually solved my problem. Or b) I still have no idea what the real problem is, but somehow the video card seems to be holding it off. I like to think it was the former... and considering what I've investigated and decided previously, I'm fine with saying it's a video card issue.
Either way though ... my freezing problem is apparently gone. I can now actually run Aero on Windows 7 and not have it lock up on me. I call that a win.