I've got LOTS of experience with this!
My advise. Don't do it, not because it isn't a cool, fun hobby, but because it is addictive and expensive in the end.
For some crack check out mp3car.com
First Car pc 1999 Pentium 120 underclocked to 100mhz with 32 gigs of ram and an 8 gig hard drive in a harbor freight case; game controller used to control song playback, Winamp as shell. Sproggy PSU
Car Pc #2
333 AMD 64 megs ram Same case, soon added added a 5.7" composite tft in dash and used a gyration mouse + the game pad. Sproggy burnt up, used an inverter.
Car Pc #3 Shuttle launched the sv/fv24 and I ordered one first day out. 1ghz. GREAT size; fit in the small harborfreight case with PSU, HDD, extra fans. Man was it cool, everybody quit calling me a geek, and just respected.
At the time there were not any good front ends yet, so it was windows 98 (then xp).
Car pc #4 Put me back in Geek; I mounted a 15" screen directly in front of the passenger; eventually added automatic brightness controls, built in touchpoint, small keyboard in glove box; head unit in glove box with face plate in sunroof pannel. Man was it great. All Got stolen, except for the screen, then I got stopped for having a screen in the view of the driver (never had an issue when it worked), and just scrapped the project.
Issues you will have are 1) ground loops 2) most sound cards don't sound that great, so you wil end up buying a decent USB one. Seriously budget 4* what you think, these things eat you alive, but man are they fun.
Edit: Answering your question DUH!
http://store.mp3car.com/New_7_Transf..._p/mon-052.htm is what you will end up with
But
http://store.mp3car.com/2008_Lillipu..._p/mon-016.htm Works well if you are not in direct sun. ( I've installed a lilliput before and they are great; but not close to the daylight readable screen above) The Lilliput guys at SEMA are funny, very very bad english.
