I haven't played TF2 that much, and the only problem I did have, was the same problem I had with Bulletstorm. Bulletstorm kept shutting down my PC in the same place in the game, so that's why the whole driver thing makes sense to me. Interestingly enough, the times when it shut down, I was hanging around this one area, ducking shooters and trying to figure out how to get past it. After installing the older DX files, when I started the game, I just plowed through the area just in case. In the end, I played for an hour or so, no problem. When it was shutting down, the longest I got to play was maybe 20 minutes at first (at the LAN party), then, literally, a minute or so once I got to that area. As for TF2, I have no idea what caused it, but I am pretty sure I wasn't getting that error.
Well, it's great we both cleared up our problems, and even better that we have a record of them, in case someone else needs help too. Have a great weekend!