Even though its an ancient DOS program it works fine for me in XP.
It demonstrates how when the motion of the image does not match the refresh rate of the monitor your brain gets confused. Real world object move continuously. They don't move-pause-move-pause at 30Hz. Your persistence of vision can deal with fusing a strobing image into the perception of fairly continuous motion. But when the motion does not match the strobing, your brain tries to re-interpret what it sees as multiple, separate, continuously-moving images. You get a kind of double-vision effect. It's wacky, but so are a lot of aspects of the brain if you study it.
To stress the point: It is not the 30Hz-ness that causes the double vision. It is the double-strobing the same image twice between each motion that screws you up.
This is why most people don't like 30 Hz games, but can't clearly explain why. Everyone notices the effect at a semi-concious level, but it is hard to understand without a clear demonstration like Marky's little app.
Both are 30fps. That's why I never bought the first PGR. I've heard PGR2 got rid of the stuttery environment maps, but I haven't seen it in motion to confirm or deny that. Forza's definitely got them, and that runs at 30fps.