One alternate approach, although not as flexible, but may useful if the primary purpose is in-vehicle use, would be to get an Atom based mini/microATX motherboard and special in-vehicle housing with nice heatsinks to avoid need for fans. Eg the Intel D945GCLF2 board, or something newer. This particular motherboard is even more OS-X compatible than a netbook (less kexts needed), although most of the "installation" is very similar. Sorry can't find links, but try Google for in-vheicle computer forums and suppliers; there's a lively community out there of people making this sort of thing at home, and various companies selling cases, 12/24V power conditioners/adapters etc.