I've set my laptop up with a remote switch. It's not that hard, as long as you know what you are doing with a soldering iron. If you can crack the case open, you can connect two wires to the power switch terminals. On the other end, you can put in a momentary switch. This would allow you to turn on, and off the laptop by using the switch.
To turn the laptop on with the ignition, you could put in a 555 timer, set to one-shot mode, and hook a relay to the output. WIth the 555 timers input hooked to the ACC wire, it'll trigger the relay once you turn the car on, and never again, until it loses power. This would be just like pushing the power button when you turn the car on, and never again until you turn te car off.
for schematics on the 555 timer, and relays.