the ballast power your lights. hids are xenon bulbs. the ballast basiclly limit the power to the bulbs. with out the ballast, the xenon bulbs would over heat and blow out.heres a link that discribes what the ballast do. http://en.wikipedia.org/wiki/Electrical_ballast
ebay is where i have got all my hids. my wife and i have them in both cars and quads. i will never use halogen bulbs again in anything that has headlights. we even put hids in my fathers john deere lawn tractor. the light out put is amazing.
and i dont know if you see it on your computer or not but when i go to reply to a post, there is a ad for hids right above the message box. Dash Z click on it, it shows the differant bulb colors