I have a laptop I'm currently in the process of installing into my Lexus. It hasn't been very hard except for having to do a little bit of soldering (annoying at best). Try this tread for an auto power-on box (if you don't care about the controller powering the laptop off as it should do this automatically anyways):
http://www.mp3car.com/vbulletin/showthread.php?t=75071 . you will still need a power source though. If you want a full solution, you can try the mp3car.com store and get the carnetix power supply which has the power supply built into it. The startup controller was good for me b/c I didn't need the power supply as I had one already. I just finished it today. Take a look at the tread and see if it is what you need. It even has a remote switch to turn the thing on and off (although I didn't need it b/c my car still has the factory power switch on the dash for the radio left over I'm going to patch into to keep it as factory looking as possible). Hope this helps.