By Xenon, are you talking a true HID with driver and ballast?
If so, you're gonna be needing a set of headlight lenses that has a clear plastic face, and a sort of "cup" that the HID bulb sits in, then has all the light emitted from being reflected off the back. If the lense you buy has the aiming component on the lense of the light like traditional sealed beams, the light pattern will be scattered all over the place, and produce a whole lot of glare for other drivers. You are technically suppost to buy a HID specific projector to get a perfect light pattern, but it has been my experience that the aftermarket projectors have at least a resemblence to aimed light.
Finally, when selecting a headlight, choose one with an ECE (european) light pattern. On low beam, they have a far sharper cut-off on the driver's side of your truck so your super bright HID's don't annoy the heck out of on-coming traffic. Some people complain that it makes the driver's side of the road dark, but thats cause they aim the lights too low so they can actually see the cutoff on the road, which isn't the correct way of aiming them...
Also, what is the temperature range on the drivers? Anything higher than 6000k is illegal for street use, regardless of the application. Anything hotter than 6000k is too blue, and anything hotter than 10 000k is suddenly into the purple color of the spectrum, which will get you pulled over in an instant. 4300k are great, a very white light, and 6000k is borderline, but still useable.
I usually aim the lamps down more than normal to help with oncoming drivers and due to the increased light output from the HID's spectrum it's stll way better than any sealed beam or halogen bulb. Just my .02
