David...yeah, I have ALOT of hardware. I have PIII 900 Mhz processors, mainboards to match, 633 Mhz processors, all Intel stuff...RAM, floppies...fans..power supplies....one thing I will suggest is building your carputer using windows 2000. Windows XP will devour any processors less than 2Ghz, which is pretty much everything except for brand new PC's. I'm not a fan of XP. 2000 is quick, stable, and reliable. None of that bell and whistle shit that makes XP so clunky and buggy.
I obviously dont have spare LDC touch screens laying around....but you can buy a 7" from www.etronics.com for 225. I'd suggest staying away from EBAY when purchasing this item. Most of the new touch screens from EBAY ship from Hong Kong..you could have customs repossess your new monitor and be SOL.
The rear LCD's need not be touch screen (keeps the driver in control)...you can get plain old LCD monitors from ebay for around 100 bucks. I'd sell you everything you need from the PC side for 75 bucks. Total PC parts, including two rear screens and touch screen would be around 500 bucks. The only other thing you'd need would be materials for the console. I'm building mine from black PVC sheet material I got from Menard's. Oh yeah, and you'r going to want to purchase a splitter for the rear RCA video connections.
Most of the Mainboards I have are built with integrated video cards, sound cards, and network cards (handy for MP3/DIVX transfer from laptop or other source).
You are right, you dont need a huge HDD to run this. 2-3 gig would be enough to serve as a DVD system. I'm doing a 80 GB drive, but mine will be mostly for MP3's. Yes, I do know how to build this for off road rigours. I am fabricating a HDD (the only moving part besides DVD-ROM drive and fans) carrier which uses R/C truck shocks for suspension. Everything else can take the beating you'r going to dish out to it. I'd probobly turn the system off if you plan on banging down the trail anyway. As long as it's fastened down, it wont hurt any of the other parts to take a beating. LCD screens are actually quite robust..they can operate anywhere from -10 degrees to 100 degrees. I would suggest building velco attached "shrouds" for the monitors if your Bronc gets hotter than 100. They are safe in the vehical down to -30 degrees. Mine will be removeable, since where I live we often do see -30 in the winter.