I'm pretty sure I'm going carPC, it's just a matter of when.
What about disassembling the new Everex Cloudbook for a carPC - $400, 1.2GHz Via processor, 512MB of RAM, a seven-inch screen, a 30GB hard drive, Linux... all you'd need would be a touchscreen (supposedly available only on the developer models).
http://arstechnica.com/journals/linux.ars/2007/12/11/linux-based-everex-cloudbook-laptop-revealed