making my own usb port

i have a usb port that i am wanting to add into my truck, i found the pin out which i found here: http://pinouts.ru/Slots/USB_pinout.shtml

my question is, where or how can i pull 5v 500 mah atleast to power this to run/charge cell phones and mp3 player's, also the + and - data, do you think i could wire av cables to that, both for left and right and hook that into the input on my headunit to play the mp3 player through my stereo?  thinking it out seems all possible, but finding or how to get the 12v from the cig lighter down to 5v 500mah is what im needing help on. so where could i pull the power from?  and any opinions on this would be great since im wanting it to work and not take out a cell phone/mp3 player or something when its plugged in.  if it works this will be molded into my radio bezel when its fiberglassed :)

You can use a 2n7805 available at Radioshack to create the 5vdc you need.  To get 500mA out of it you'll need to ground the heat sink to the chassis of your vehicle. 

You can't connect the data lines to anything that isn't a USB signal (which your A/V outputs are definately not).

so than basically all i could do is use it for power.

in that case this would be the best bet, lol.. saves alot of work on everything.

http://www.pc-mobile.net/ck203.htm