Why we're so limited to static data is beyond me.
Well, it's a lot easier for a mechanic to replace a DVD than it is to replace a hard disc drive (these are car mechanics, they like big bolts and heavy equipment, not small and fragile electronics)
Hacking the system to run on Linux is NOT an easy task, probably you'd have to make your own distribution from scratch
, which is hard by itself, but not having a proper keyboard, mouse and display on the target system makes it even harder.
I'm a proffesional software engineer and part of our compagnies OSOS group (Open Source Open Standards) And I have a LOT of trouble hacking my Tomtom, and that comes with Linux shipped on it, the computer in the Civic is a Windows CE device, so getting Linux on it would take a LOT more time.
If you want to start hacking, I'd probably start by examining the disc that came with the Civic, maby you get lucky and find that it is a (relativly) standard computer, that would make hacking it easier.