If you put HID bulbs in halogen reflector housings your light output will be messed up. They will be bright, but the beam pattern will be all over the place. High beam isn't as big of a deal, but not low beam for sure.
HID's will work -ok- in Halogen projectors. They won't make full use of the increased light output, but at least it won't blind everyone on the road.
A proper retrofit will have projectors that are matched to the HID bulbs.
Those headlights look kind of goofy once they are on the car. The ones that have the side lights all in one unit look much better and generally come with halogen projectors for the low beams.
My truck has that style and the projectors work OK with HID bulbs. The cutoff is intact, but there isn't nearly the same width as a proper retrofit. I've already ordered FXR projectors as getting those in is the next step