Guys, you need to read up on the FAQs on MP3car.com. They will reveal everything you need, from touchscreens to power. They have been there, done that, blown it up and rebuilt it better! I really suggest that you go look at leemiks car on there, its a 350z and very nicely done.
As for the Zed - you can fit a 7" touchscreen in the Nav cubby if you take the surround/bezel off the screen. For power there are loads of CarPC PSUs specifically desinged to power your Pc and screen, with auto on off and loads of other options. I have a Carnetix P2140, which does all of that, has 185w of power (more than enough for a carpc), and can be monitored from the USB connection