If all you want is Xenon lighting with almost the same color as the factory H.I.D. lamps, then, like xnsf said, all you need to do is buy a pair of Xenon bulbs and swap them for the halogens (roughly $50 or less/pair). If you want to change to H.I.D.'s, that's a completely different (and expensive) story. I recommend you try changing the standard halogen bulbs to Xenon charged bulbs first (Sylvania/Osram SilverStars, for example) and see if you're happy with the difference before you think about sinking a small fortune into H.I.D.'s. I have Xenon replacement bulbs in one of my cars and they make a huge difference from the stock halogens.

There are four or five pages of excellent background information on H.I.D. lighting and retrofits at this website
http://www.sigmaautomotive.com/HID/hidfaq.php