Stupid point, but do these use OpenGL or DirectX?
I can never remember what way around it was, and I guess it's not wholly dependent on the above anyway, but a friend of mine got really bad headaches / sickness from some games and not others, and it turned out it was because the ones causing the problems had a very slightly (few ms) longer delay between him moving the mouse and the action happening on screen. Wasn't enough to notice when you're looking, but turned out it was enough to send him over the edge!
I suffer with this generally while playing 3D games to the point I can't really play them at all these days. I probably could if I got used to them perhaps, but I'm not a huge gamer anyway and going through that feeling a few times just for the sake of it isn't my idea of fun!