To borrow a phrase from saturnina, "I feel like ass today." Not enough sleep. When I finish work today I will be taking a nap. Yes, this is the exciting life I lead.
It looks like my hunch about the old video card being the problem is right. The memory diagnostics are coming back clean. Of course I'll let it run overnight to be sure.
This is what I get for trying to rush things and use an unsupported old piece of trash to "get by in the meantime". I should know better.