I could tell you how to do it the cheap way but thats the wrong way.
Hell Im bored so ill tell you about projectors and stuff since no one else did
Projector lenses consist of three parts: a shield, reflective surface, and concave lens. The light in effect bounces off of the reflective surface and passes through the lense which focuses the light. Depending on what bulb you use(HID or Halogen), the bulb must be in a certain position for the optics to be accurate. THAT IS WHY YOU NEED AN HID PROJECTOR LENS for HID instead of a halogen lens -- because of the differences in positions of the capsule of an HID bulb and the filament of a halogen bulb.
The shield is used to cut off a certain direction of light. If you look at the light emitted from a projector lens,the point where light is emitted and not emitted is sharp like a knife. You will also notice the "cutoff region" in an HID projector has a distinct blue/purple line. This is what we perceive when looking at HID light, and this line is what gives all those HID cars that brilliant purplish light.
So to do it right you're going to have to either look on eBay for HID projectors and retrofit them into your existing housings, or look on brightheadlights-hid.com for a xenarc silvania system. I suppose between the time of this post and now you've gathered some info.
If you do it half ass the glare is going to be horrid and you will blind drivers/get tickets/looks like a ricer/fool in the process. Your stock units are not equipped to handle the excessive light an HID capsule puts out.
Hope I dont sound like a know it all, just tryin to give you some good ideas and info, cause at one point or another I was in your exact same position and I had to learn it the hard way experimenting, because no one knew shit back then or they didnt offer it when i asked. well good luck dude.