That idea's not going to fly very well, as least from a practical standpoint. You can read the following thread-
Ecost.com (and some others) still sells the wall station, FWIW. I see it as a little out of date for the money you would have to pay though just to get ethernet. For the same price you could upgrade to fairly decent audio equipment like a receiver/DVD combo which you could network to a PC, etc. Why mess with the car stereo in wall when you can upgrade to a better device or devices for the same money and less hassle.
I had this Sony WallStation that unexpectedly stopped working. They don't make these anymore, and ones that I can find are expensive. There are not a lot of choices out there, or at least ones I like for In-wall installations. I have pulled it out before and it uses a 12-volt Dc input (and has some power surge thing for it too), + and - left and right speakers, coax for Fm, had nothing but uses the standard thing for AM, and L/R RCA inputs. It also had an ethernet port but you ain't gonna find that in a car stereo. I was wondering if the original wiring is ok to just drop in a double din, car stereo in it's place. Is this a good Idea. If I lose the RCA input it won't be a big deal.