I have just installed Carputer in my E46.
I will share my setup when I am free.
Dont have much to say..jus imagine having a full working computer in your car, at your fingertip, literally coz using TOuch Screen. Hehe

(I am facebook addict, now i can fb'ing when driving. LOL. Warning: dont do this at home)
Integrated GPS module, with reverse camera, WIFI, front end software, special power on and off using automotive dc dc power supply.
basically, you can do whatever you can do with your desktop/laptop pc, but in your car!
I even installed game and use wireless game controller for passenger.. but u'd have to stretch your eyes coz the screen is 7" ^-^
Anyone interested can drop me a pm, actually i own a computer shop and i m thinking of installing carputer to our fellow e46 (yes, only e46 as it would be easier for me coz i have done it once!)
I m doing this in my free time only, i have other job on weekdays, so expect some time for me to reply k..
You wont need ipod or cdchanger as your memory is as good as your hd capacity. for me, i have 1TB harddisk installed!
Cheers.