I'm pretty new to this car pc stuff, but I'm helping my son build a bonneville, complete with touch screen. I'm a savvy tech guy for the most part, but we went with a standard ATX motherboard I had laying around my shop. We have a boot image for XP on a 4 gig thumb drive, and set the MOBO to boot from USB device. It was 9*f here last night, and it was booting just fine. We have a removeable usb hard drive that contains media files. I will admit it boots slower off the flash drive than it does a hard drive, I assume because it's building a ram drive to hold the OS.
Just thought I would throw that out there. I've got a ton of questions to ask around, but thats been our solution for now.