Solid idea. I've been thinking a lot lately about the iPad as a car computer. This adds a great new dimension. Here are my thoughts:
The iPad is certainly an awesome interface for a CarPC. Unfortunately, remote-ing into your Eee will diminish the simplicity of that interface. We can come up with some software to make that easier.
On the simplicity of setup, using the Eee as a host will make things much nicer for the iPad. You'll be able to put the iPad into the car freely whenever you want, and have it jump on the network to control - MUCH cooler than having the iPad permanently installed in the car.
I might pick up one of these soon - http://www.mp3car.com/blogs/142586_i...ion-mount.html
Using VNC or Teamviewer (my favorite) on the iPad might get clunky and annoying. Even with a strong AdHoc network, you'll be streaming a full display.
If you could make a native app or web app that shows the OBD info and your camera feeds - and host this from the Eee (web app).. That would be SO COOL.
For music, I would use the iPad as a remote and control iTunes on the Eee.
For videos, I would use AirVideo. But then you'll have to have the iPad connected to your stereo directly.
For Navigation - I've found that when using MyWi (jailbroken iPhone app) to tether my iPhone 4 to my Wifi iPad 2, my iPad actually pulls the navigation coordinates from my iPhone! If you can put a GPS dongle on the Eee and have it share the location data to your wifi iPad, you could use Maps or MotionX GPS Drive on the iPad... (if you have an iPad 3G, you've already been blessed with GPS on the pad).
This might be the best solution for using the iPad as a front-end. If you are a programmer, building a native iPad app that could interface with the Eee would be a killer option. Otherwise, a web-app could do most of the things - and you'll still be able to have a simple interface.
If you really want to go the Remote Desktop route, use TeamViewer. I have found it to be the cheapest (FREE) and best solution available.
Keep in touch! I'd love to see the project if you take it on.