A car computer (carputer) is an awesome system to install in your car. Not only can a carputer play music and videos, but you can also install navigation software, browse the web, download files, or do anything the PC you're using can do. However, many people don't know where to start, or they don't have the first clue as to what a carputer system consists of.
Here are some general tips and suggestions to get you started on your build. I know that when I was starting out, I had to learn the hard way by studying MP3car.com's forums. By the way, if you want to see carputer setups, want more info, or anything carputer related, MP3car.com is pretty much the defacto resource.
Touchscreen Double Din
Motherboard/CPU:
Most people choose a mini-ITX form factor motherboard. Mini-ITX motherboards measure approximately 7" x 7", usually come with a CPU, and consume less power than their full size ATX counterparts, which make them great candidates for carputer usage. Mini-ITX motherboards come in lots of different configurations; there are some boards for Intel, some for AMD, and some are VIA based. Some boards can handle up to Core 2 Quad core CPU's, but expect to pay mucho $$$ if you want that level of performance.
For carputer usage, you're most likely not going to be encoding media, playing games, or running tank terrain simulations. Popular choices are the VIA C3 and C7 mini-ITX based motherboards, but they are being phased out by the growing popularity of the Intel Atom boards. Intel Atom processors are widely used in netbooks, but their low power requirements and low heat build up make them perfect candidates for carputer usage.
A very popular, best bang for your buck motherboard would be the Intel D945GCLF2, in my opinion. Not only does the board run cool, it also sports the dual core Atom processor, which in my experiences, is more than fast enough for carputer usage. Also, at less than 0 for both the CPU and motherboard, the deal is too good to pass up.
Power Supply:
The easiest, headache free solution is to use an intelligent DC-DC power supply. Intelligent power supplies have integrated startup/shutdown controllers that can sense and power your computer when you turn your car on/off. This is very important, because if the power supplies were "dumb", you would have to manually turn the carputer on/off every time to enter and exit the car. See how that can get annoying?
Intelligent DC-DC power supplies usually have a number of wires to be connected to your car's electrical system. This includes, at the bare minimum, a power wire, ground wire, and a remote wire. The remote wire is wired to a 12v source that only becomes active when your key is in the ignition. The most common usage is to use the remote wire from your CD player/head unit, that way, when the CD player turns on, so does the carputer.
As far as brands go, I would go with Opus. While they are a little more expensive than the M2/M3/M4 ATX power supplies, they are of higher quality. I had an older M2 ATX that would only put out 10.9 - 11.4 volts on the 12v rail (not good!). Since then, I replaced it with an Opus 120w and it's been running strong since 2006. I've also heard good things about the Pico PSU lineup. Pico PSUs are very small and connect directly to your ATX power plug on the motherboard taking up very little space. I would use a Pico PSU if you're extremely cramped for space, like in a glove box build.
Hard Drive and Optical Drive:
2.5" notebook hard drives are the most popular because they are small, use little power, and are rugged. 2.5" hard drives are built to take the everyday vibrations and shakes it would experience from being in a laptop, so it would make sense to use in a carputer where you'll be running over potholes, hopping curbs, etc. I've been using an old 2.5" 80GB IDE for at least 3 years now. I've dropped the hard drive multiple times and have it mounted pretty badly, but it's still running strong! 3.5" hard drives need much more power, and power is precious when we're talking about small, 90-120 watt power supplies.
Optical drives; who uses optical drives anymore? The only time I used an optical drive was for the initial operating system install. Even still, you could probably get away with installing your OS from a USB flash drive. As for daily use, I guarantee an optical drive would receive almost zero usage. Your music should be on your hard drive and a USB flash drive can be used to transfer files. The only thing I can see an optical drive being useful for is to watch DVDs. However, how often are you actually going to sit in your car and watch a DVD? The only time you can think of doing so is either when you're driving, or when you're stopped. If you're driving, do you really think it's a good idea to watch a movie on the way to work? If you're stopped, wouldn't you rather watch the DVD on your big screen in the house? At this point in our technological evolution, optical drives are becoming more and more of a novelty.
Memory:
Get the cheapest, highest capacity you can find. I have 1GB in my carputer and it runs pretty quickly on a full Windows XP install (I'll get to this later). 2GB would be even better, but it's not really necessary and I doubt you'll see a speed increase.
Enclosure/Case:
Despite what you may hear or think, a case is completely optional as long as you have your components mounted somewhat securely (meaning they won't bounce around like crazy while driving). Mini-ITX cases do exist and can be found at stores like Mini-box, MP3car, and Newegg. If you have the space, a slightly larger (but cheaper) micro-ATX case could be used instead.
Here's some proof to backup my claim that a case is optional. I've been running my setups in the glovebox like this for over three years with zero failures. The CPU temperature settles at around 50-60c depending on the outside temperature. The hard drive is mounted to top of the glove compartment using double sided adhesive. The motherboard and power supply simply sit on a peice of cardboard.
Operating System:
My advice is to run a full version of Windows XP instead of a "custom" XP build such as TinyXP. TinyXP is basically a stripped down Windows XP install which takes up less disk space, less memory, and loads a bit faster than a regular Windows XP install. However, I've noticed that TinyXP isn't perfect and is definitely not for everyone. Drivers are stripped out, services are missing, and in my experience, it's not the most stable OS either. Do you really want perform advanced troubleshooting for some odd program you want to work? Save yourself the headache and install a full version of Windows XP. Even on just 1GB of memory (2GB seems to be the standard now), XP runs silky smooth.
Then we come to the issue of whether to fully shutdown the computer or to have it hibernate when you turn off the car. Hibernation basically takes all the information present and stores it on the hard drive when the computer is turned off. Then, when the computer is turned on again, the data is restored from the hard drive and you're back to exactly where you were before you turned the car off. As nice as hibernation sounds, it's not very reliable in my experience. My hibernation image becomes corrupted every 10-20 or so startup/shutdown cycles. So, do yourself a favor and fully startup/shutdown for every session. A carputer on a full install of Windows XP doesn't take long to boot anyways, plus, it saves you a whole lot of headache in the future.
Front End:
Using a front end is completely up to you. The front end is basically a finger friendly program which contains all your media controls, media player, etc. It pretty much makes your carputer look like an Alpine or Pioneer double DIN touchscreen unit. The two most popular front ends are Road Runner and Centrafuse. Both are great players, but both have their negatives.
Road Runner is open source (free), but is a pain to setup correctly, and in my opinion, is too cluttered and doesn't look as good as Centrafuse. Centrafuse, however, is not free, but it's extremely easy to setup and works great right out of the box.