I had thought about that also but how annoying would it be to wait for the OS to boot up every time you start the car?
If you use an intelligant psu (boots the pc up when you start the car, and shuts it down when you turn the car off), and set the pc to hibernate rather than completly shut down, i managed to get mine to boot up before i had got to the end of my road (bout 300 yards).
tbh, as cool as a car-puter was, it was a bit of a pain in the
It was cool to have one, but i don't think i'd bother again. I even used specialised software called "mobile impact" so everything i wanted was under one easy-to-use interface (which wasn't always easy
)
If anyone asks me for advice on getting a car-puter, i always say get one of these-
http://www.cartft.com/catalog/il/512
Bare in mind that the price listed is only for the barebone system, but for about £700 i think you can get the din pc, a monitor and everything needed, even gps included as well.
Its a lot less hassle to fit one of those, and in theory overheating problems should've been dealt with already, by the manufacturers.