If you're smart, you don't. "HID kits" are widely available, but they are (all) illegal and dangerous. See the related link for a detailed explanation.
HID headlights refer to high definition headlights. These are headlights that use LED lightbulbs in them so drivers can see clearer and farther ahead in the dark.
You could find information about hid headlights on Wikipedia, at http://en.wikipedia.org/wiki/Headlamp. Hid headlights are usually attached to the front of a vehicle like a car or motorcycle.
...If they're hid, what difference does it make?
HID headlights are far more brighter than normal Halogen bulbs that are normally in headlights. HID are often thought of as safer because they have a blue glow to them and resemble daylight more than normal bulbs.
There are a couple of reasons why a 1999 Tahoe headlights may not work. A couple of reasons could be blown bulbs or the wiring.
No
From what i understand, HID kits are illegal unless you have a projector installed on your car so it controls the light output of the HID's. Projectors spread the light evenly and have a cut off point which don't blind on coming drivers. Don't just install the hid kit, replace your headlights with projects =)
of course
No. the headlights are terrible. I would be better off with a set of candles.
There are screws
headlights
You can buy HID headlights directly from your local auto parts company, or your main dealer. Failing that you can try sites such Carhidkits, eBay or Amazon.