To my understanding, most states it's illegal to have HID outside of a vehicle that was originally equipped with them. With your Explorer, it's understandable. There's no way to keep the light out of people's eyes. Most OEM HID's are in projectors. The projector has a cut off shield that does just that, it cuts off the light from going ot high and blinding people.
I've done extensive research about HID retrofits and IMO, retrofits are the only way to go. A little costly, but they're well worth it.
But, I can't talk too much... I have an 8000K kit in my xB, but it has non-HID projectors.
I don't suggest anything higher than 6000K. My 8000K kit is a little difficult to see in the combination of rain and dark.