I just made it up. Deal with it.
My computer had developed a habit of suddenly restarting while playing Civilization. I thought it might be overheating because I hadn't put back on the side panel of the computer, with a fan in it, which might be the main source of incoming air. That didn't fix it and I didn't really think it was overheating anyway, based on the "touch stuff and see if I get burned or zapped" test yielding negative results (in the diagnostic community, negative means positive, which is the least confusing thing we say).
My next suspicion was a bad stick of RAM. So I did the logical thing, switched them into the other pair of slots. That didn't fix it, which confirmed my suspicion.
Finally I resorted to pulling out one of the two 2gb sticks and replacing it with a pair of 512mb sticks from my old computer. This wasn't as big of a loss as it sounds, since Windows only seemed to recognize 3.5gb of the supposed 4gb total, so I only lost 512mb. Maybe there is some performance impact from having the unpaired stick, but I've not noticed. It is certainly offset by the reliability gain.
Coming tomorrow, plus or minus a month, Skyrim!