The following is a supply list for my personal suggestion on how to go about making a car camera mount; for other ideas, check out the next page of this article.
Screw/tripod mount. Since the car's going to be speeding along at a tidy rate, that camera needs to be bolted down or there goes a rather considerable investment on your part! So, you'll be wanting to mount your camera with the stablest method possible: via the tripod mount adapter on the bottom of your camera. Preferably, you should cannibalize a tripod mount from an old tripod, as that will provide the best possible swivel and angle control of the camera, but failing that, you can just use an appropriately sized screw from the local hardware store (which you will need anyway to attach the tripod mount.) Make sure to bring your camera along to check the fit!
Stick that is sturdy, thick enough to take some drilling, and of the appropriate length for where you will want to place your camera in the car. Metal looks nicer, but using a strong piece of scrap wood will do just as well, if not better: not only will it save your drill bit some unnecessary screeching and is probably just laying around the house anyway, but this also makes it unnecessary to thread the stick, which you can't do with everyday tools anyway.
Alternatively, if you're planning on using an old tripod, you could just keep deconstruct everything except a portion of one leg and the attached tripod mount for this. (If you really want to rough it, you can just strap your tripod sideways to the passenger head rest struts, but we're looking for something a bit more stable than that!)
Drill. You're going to need to bore a few holes, and depending on the material you've chosen for the stick, some metal could be involved, so make sure you have a drill bit that is appropriate. With metal, you'll also want to have a device to thread the metal for use with the screws. You'll want the drill bit to be slightly smaller than the screws if you're using wood, as you're going to be creating your own threads on the inside by screwing in the screw manually.
Four screws & wing nuts. It's easier if these are the same size at the one that attaches to your camera, but not entirely necessary. If the screws have big heads, you can forgo the wing nuts: the idea is to interlock the ends of the screws to ensure a tight fit.