hey just found this thread, what a fantastic idea with the car-pc!
i might add a couple of improvements tho, firstly you could get a USB 802.11b/g wireless card... you can get external antenae for them also to improve reception, hence eliminating the need to transfer files/data via a cd drive or usb key. Obviously secure it or disable it when you dont use it!
next for those who are having issues booting off usb, you can buy things called Disc On Modules which are in effect, flash memory built into a 40-pin IDE connector.
So you plug it into the HD connector and it should detect as a HD... havnt seen prices for anything larger than 128mb, but they say theyre available up to 1.5gb. Keep an eye out for them, they may be the next cool thing.
As for speed with flash memory well there are pros/cons, most memory has extremely low latency (fast seek time) but transfer speeds are low compared to HD's. Also they have no moving parts. So would be great for opening/moving small files, but churn with large file copies etc.
I've also heard of some ppl using mini-ITX boards with Compact Flash adapters onboard. Lots of modems/routers use this method for booting skeleton versions of Linux, but I cant see why Windows couldnt work. Compact Flash cards can be bought in sizes up to 3-4gb im fairly sure.
Anyway nice work to those who have made them, got me motivated for when i look at stereos in my car