Woohoo, I've just ordered everything I think is necessary for my car PC system:
Xenarc MP-FL8 with DVD-ROM and 512 megs
Xenarc 700TS 7" touch-screen
Carnetix CNX-1290 power regulator startup/shutdown device
Globalsat BU-353 SiRF-III USB GPS
Small USB hub
No-name Chinese USB sound dongle to give me optical TOSLINK out
The Xenarc was the only system I could find small enough to fit in my glovebox. (All of the DIY cases like the Ampie are way too large).
Haven't decided on a hard disk for the PC yet... since I'm going to use this primarily for serving MP3s I may buy a 100gig or use an existing 60gig I have and maybe hook up a big external 3.5" drive over USB.
The optical out is going to my aftermarket car stereo system which is contolled by an Alpine PXA-H701 processor. The major impetus of this car PC setup was that there are no MP3 players currently shipping that have optical out.
All of the wiring necessary to hook this into my car is not a problem, after spending 3 months redoing my entire vehicle for a competition stereo system I can do this in my sleep.
I'm also thinking about adding a wireless USB network dongle so I can connect to the PC while the car is in my garage (accesories on and hooked up to a 40amp battery charger so I don't kill the battery).
I also have a Treo 650 phone in my pocket that supports bluetooth DUN lan hookup... if I buy a bluetooth dongle possibly I'd be able to have internet access anywhere I drive (for a price of course).
The LCD I hope to mount somehow on my dash. I already have a ProClip dash holder for my iPod superglued onto my trim already. Hopefully I can somehow affix the screen to that.