Well, I've done a lot more work... back to running 4gb memory, new video card installed and working, every windows update is installed, every hardware driver installed, MCE is fully functional, about 75% of my apps are installed, and the system is 100% rock solid. Not a single issue in over 3 hours of intensive use, compared to crashing even while loading the emergency console!

I think important but not crucial parts of the registry had become corrupt on the old installation, and uninstalling the video card made things worse.

I notice that some minor things that had been a bit quirky on my system since day one aren't there any more... for instance if I was viewing a folder on the hard drive and used the Favorites menu to select a site, it would open up two IE7 windows. Doesn't do that now.

There's a few other quirks I had that I'll check out as well...