So far the dashpc yahoo-egroup seems to be the best place to talk about this kind of stuff:

http://groups.yahoo.com/group/dashpc/

You can search the archives to find a high-quality 12-volt (non-switching?) PC power supply I think it is about the equivalent of regular 150 watts, or maybe the price was $150, not sure which...

Myself, I've been thinking of putting a 10.4" or larger 1024x768 tft touchscreen in the dash too, I think it is going to require some custom fibreglass work. I am thinking about removing the head unit, halving the height of the vents and then putting it in at an angle. I am still looking for the right display, I want one that has adjustable brightness up to at least 600-800 nits with at least 1024x768 resolution.

I think I will get one of Tone's rear lockers and use that to house the computer, running digital video (either DVI or LVDS) to the panel in the front. I also am seriously looking at distributing 6-8 miniature CCD cameras around the vehicle for surveilance, precision manuovering (aka 'parking in tight spaces') and anything else you might do with all those cameras. I've found a hardware mpeg4 encoder board used for security cameras that can handle up to 16 video sources simultaneously and it claims the software can do motion detection so I'm thinking it can be set to record only when people actually come close to the vehicle.

I am also looking at using an m-audio sonica theater usb based 7.1 channel decoder to drive a bunch of Bohlender-Graebener ribbon speakers via blaupunkt digital amps (almost 100% efficent so little to no heat and very small and light-weight). I have fullsize B-G speakers at home and love their sound quality. I'm still contemplating mounting the 8" ribbons in the A, C and D pillars, I think the A's will be the hardest due to the slope, and then what to do with the front center - in the dash I guess. I think I'm also going to need 700Hz x-overs to go with them for mid-bass re-inforcement and accompanying traditional drivers to go in the current speaker mounts - I think I will let the D-pillars just use the sub (in the rear-tire well) for bass reinforcement. The sonica has good, per speaker, bass management and should be trivial to upgrade to future generations. I wish it were 11.1 channels so I could do all my x-overs in the digital domain, but I doubt that even the next couple of generations will have that many channels.

Of course I plan on hooking up a GPS receiver and using some sort of mapping/directional software. Also I want to plug into the OBDM and at least track car status information. I'm planning on putting both firewire and usb2 hubs in the dash below the LCD for in car temporary hookups, will probably also stick a firewire DVD drive in the dash to play the odd music disc and maybe a movie (though I don't really buy into the in-car theater system, other than as a child pacifier and I have no kids to pacify) Wireless 802.11g 52mbps ethernet for in-garage connectivity and maybe war-driving. Some sort of cellular type system (gprs, aprs?) for on the road connectivity (my own lojack, car gets stolen, it takes a picture of whoever is in the driver's seat along with images of the surrounding area whenever it stops moving and then emails that along with gps coords to me).

I'm trying to make up my mind between going with a VIA EPIA-M1000 system, it has everything, including LVDS video on the board, 1GB of ram, ethernet, IDE, USB2, FireWire, etc -- but only 1 PCI slot and the 1ghz Nemeiah cpu is slow, but ultra low power, so minimal cooling and smaller power supply and the board is tiny, only 6.5x6.5 inches. Or a larger, faster, hotter board, if someone would build a micro-atx board with all the features of the EPIA but 3-4 slots and using one of those new speedy but low-power Pentium-M chips that would be ideal, but I doubt anyone is building them, a least not for general purpose use.

Either way, I think I am looking at a second battery at least to power it when the car is off without killing the main battery plus the benefit of being able to survive one of those fuse blow-out attacks by car thieves that people have been talking about in another thread here. Maybe a roof-mounted solar panel to trickle-charge the system on sunny days too.

Some things I don't know if are possible but I think would be totally cool:
I'd really like to use a second LCD display to replace the gauges and go for the fully programmable digital dashboard, or even cooler, get one that is super bright and use it to reflect off the inside of the winshield as a HUD. If that could work it, I think it would need a replacement windshield with a special reflective coating else you get double-images (one reflection off the inside of the glass and one off the outside of the glass). I think all the information needed to do a digital dashboard is available via OBDM.

Anyways, that's what I'm thinking. So far it is only talk because I am a super procrastinator (and a leg injury that has kept me almost house-bound other than work for the last couple of months while I try to let it heal-up). But I certainly welcome any comments, suggestions or warnings. I can assemble a regular PC in my sleep, but my experience with 12-volt car systems is pretty limited, so I could easily be missing something major here.