According to the US Department of Transportation, any HID mod into a stock housing not designed for HID is not for use on public roads. This is defined as a "colored light modification" under many state laws and is therefore illegal. I install HIDs at my shop in MD, and I have to add a clause to my work orders that says "HID conversions are done for off-road/show use only" to address customers who insist on getting the bulbs put into stock halogen housings.
Now, most cops won't pull you over just for that. But, I have seen it happen. A guy I know had an HID setup in a 2002 F-250 with the stock housings. Cop pulled him over and issued him a citations for illegal modification(s) and unsafe vehicle operation (due to the glare blindng oncoming drivers).
If you want to do it right, you need to either buy or build a set of projector housings. These will focus the light correctly down the road with the correct cutoff. Hope this helps!