software that runs on XP will run on XPe, including drivers. XPe differs from TinyXP in that you build an image from the ground up from a choice of thousands of components, including custom components you can make yourself. In addition you have a number of deployment and servicing options that make managing numerous devices a lot easier. XPe is really meant for commercial devices, I don't think the development time is worth the effort for your single carPC. On the other hand, 2011 is much better and a cleaner, easier development experience so I would definitely recommend that even if it's still pre-BETA.
EWF, HORM, MinLogon on XP.
Zotac ION Atom N330, 2GB low-profile RAM, M3-ATX
Win Embedded Std 2011 RC
OCZ Vertex Turbo 30GB SSD
Lilliput 629 Transflective, WRX Screen Mount
BlueSoleil BT, i-Blue GM-2 GPS, DirectedHD Radio, Andrea Mic