Relays was the first thing to come to mind when I thought about switching on lights... but now that I think about it the headlight switch in my care is most likely connected to a relay. I will have to measure the amperage across the switch I am pretty sure it just a +12v signal so I could use a transistor. What would be the easier route?
The X2 meant times two as in I need two temps sensors. I just ordered these off Ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=171270756674&ssPageName=ADME:L:OC:US:3160
This $55 "RF8315RT Active RFID 8 Meters Transmitter and Receiver" is good upto 8 meters but it does not work within 1 meter 
http://www.ebay.com/itm/RF8315RT-Active-RFID-8-Meters-Transmitter-and-Receiver-/291120081442?pt=LH_DefaultDomain_0&hash=item43c81bea22
The whole point of the RFID is so I can walk up to my car and it unlocks with no intervention and when I leave the car it locks with no intervention. Is it possible to us Bluetooth or 433Mhz TxRx in this fashion?
Thanks for the info about the "9 or 10 DOF-module"... this could come in handy in the future when I use the Arduino to drive the car 
The headlight portion of the code will be blocked off in an if statement checking for +12v from behind the cigarette lighter plug which turns off when the car shuts off so I don't think I will have any issues there. I also will program it to wait 10 minutes before turning the lights on when it gets a "dark" signal. This way it will not flicker when its on the threshold.
I guess my only other worry is the Arduino will drain the car battery after a week of no use. I was reading about code to make it enter low power states but I need to research that more.
Thanks for the help Simpson_Jr!