Was thinking of buying an incarpc from www.incarpc.co.uk , but decided to do it myself. It says on the website ...
Can I have extra displays installed so that my passengers can use the computer as well?
Yes you can. We can install additional displays in your vehicle so that passengers can use the system as well. For example, if we installed 2 screens in the rear of your vehicle then one rear seat passenger could watch a DVD while another rear seat passenger browsed the internet or sent an email. The driver's screen would be unaffected by this, and would continue to provide, for example, navigation information.
How on earth can i do this off just the 1 computer?
By setting up some variant of terminal services/remote desktop connection.
The cpu doesn't care how many sessions you slice it into, it's the job of the OS to determine how that works. Of course, having 3 people whack against the processor/memory/disk subsystem of the computer = slower than only 1 person watching a DVD..........
Just make sure that your base hardware is strong enough to handle the amount of work your asking it to do and you'll be fine.