I once deathmatched against someone at a LAN party who played Quake in a tiny little window on his screen. The window size was about 2 inches square. That was his solution to preventing motion sickness. It worked really well for him, and he was a fantastic player, constantly winning matches. I'm pretty sure you can run those games in a window and set it to any size you like. You might have to fiddle with the game's configuration files to make it smaller than 640x480. But maybe 640x480 in a window, combined with sitting back from the screen pretty far, might help?