Older thread but I'll reply to it. First off you want the most useable light possible, and an 8,000K rating is not going to give you that. Stick to the 4300k, 5000k or 6000k (white with a hint of color, but pure white) so that you can be sure you are seeing the best.
Second, you NEED a relay harness. You cannot run HIDs on factory wiring systems without this. It will melt your factory harnesses and potentially set fire to the multifunction switch.
VVME.com sells good kits at really cheap prices. Thats where I got my foglight kit from, and my replacement ballast for my headlight kit. I have a relay harness for both my headlights and foglights and have projectors for both (the only real way to run them). HIDs in halogen (factory) housings only throw light all over the place except where its supposed to be.
Single Xenon is low beam only. Bi-Xenon is high beam and low beam. I.e. if you have a Dodge Neon with a 9007 application your highs and lows are on the same bulb. You would probably want a Bi-Xenon kit. Whereas if you have a Pacifica or a Crossfire you have different bulbs for high and low beam, so a single xenon kit would be better for you.
Hope that helped...if you have any other questions, shoot me a PM or ask on here. I have retrofitted headlights and done all my installs myself...so I'd be happy to help you as best I can.