Finally we get the last game in the series, an excellent one too. With beautiful 3D graphics I can get my money's worth out of my video card :-)
A word for those of you who are suffering from headaches or generally feeling sick from playing this game or any 3D game for that matter.
I looked it up and turns out I'm suffering from a phenomenon that's called Simulator Sickness which is same as motion sickness like you get on bus rides.
My tip for any of you who are experiencing the exact thing is to change the rendering engine from Primary (3D accelerator) to Software. Although it will look less appealing visually and may be a tad slower, it absolutely *does* take away the symptoms.

A lot of this is usually down to framerate and/or refresh rate issues.
If your hardware can do it (your monitor), either by picking a lower resolution and/or just forcing it in your video card control panel. Getting your refresh rate up above 60 mhz is highly recommended. I have a nice viewsonic monitor that I can get up around 75 mhz. 3D televisions coming out these days can get up to 120 to 200.
If you're a chronic sufferer of veritgo/motion sickness however the only cure is small doses, don't watch the bright screen as a single light source in a dark room, and as a final resort stick a small white dot (not permanent) in the middle of the screen as a fixed point of reference for your eyes to focus on. At first it might seem to worsen the effect but eventually it gets better. It was the only way I was able to get through the Descent series.

Thanks for replying!
Everything you said is correct, however I have an LCD monitor so refresh rate is not the case.
What causes the problem, which I got from reading in Wikipedia, is that the game environment is too realistic and that causes the brain to think we are in motion, thus by reducing to software rendering it becomes less realistic and easier on the eyes.

I've heard that you can reduce nausea by keeping the lights on in your computer room, or by eating ginger (raw or cooked, like ginger snap cookies). It also helps to back away from your monitor a little.