The easiest way to do this would be to run two parallel installations of Windows, one with the old drivers, one with the new. Which would be a giant pain to set up and maintain just for a single game.

I just find it kind of strange that a game won't work with a newer version of the video drivers. That shouldn't happen, period. OpenGL and DirectX are both backwards compatible in their APIs so a game written for OpenGL 1.0 should work with a driver using OpenGL 1.4 and the same for DirectX. And for the most part, all the video driver does is just send the data along to the video card to be processed, then hands that back to the game. Something seems a bit fishy if the game won't work with newer versions of the drivers, but have you checked to see if there's an update for the Far Cry game? Maybe they fixed this little problem in that update.