Please, please, please don't just put in a set of 9007 HIDS. Not only is it illegal (I'm dead serious), but it's not the greatest choice for lighting. Regular HID sets were not designed for halogen housings unless specifically made OEM right from the factory (Cadillac for example). Most cars use a projector with an HID system, which is the ONLY way to go (again, unless it was factory like BMW or Mercedes).
Halogen housings and reflectors were designed for just that.....halogen bulbs. ANY halogen bulb is best, an HID system is NOT. Since the bulbs are completely different from a halogen, things such are glare, dead spots, and hot spots will be MUCH worse. Sure they'll look all nice and superblue and cool, but they're honestly not the way to go. This isn't bad for just you seeing the road, but much worse for other drivers as well.
The best thing to do is just use high quality halogen bulbs, get an additional set of driving lights, or do what's called a "projector retrofit". Which means custom installing a set of projectors inside the stock lenses, and then a set of HIDS in those if you wish. It's not easy, nor is it cheap, but the ending results will honestly be 10x those of a "drop-in" set of HIDS, and 100x that of a halogen system.