It's easy enough to fit aftermarket HIDs, there's a couple of 'How To's' on the forum.
They can be fitted to the standard halogen reflector housing but make sure you get H7R bulbs, not the regular H7's.
Technically you'll need to install auto-leveling and a headlight washer system to make them legal which would be a big job.
As above, don't get a cheap kit off eBay. You'd be better off spending a little bit more and getting a good quality kit from a reputable supplier.