I've heard of people installing a computer in their cars for music or other reasons but I'm wondering if anyone here has ever done it or has info about how to go about doing it and what parts to use.

I haven't built one, however I've thought about it, and I have afew tips:

-It's called a carputer, or CarPC, so googling those will help you out a lot
-You should use laptop hard drives, or Solid State Drives, over standard 3.5" desktop hard drives; reason being is the fore-mentioned disks are more resistant to shock than standard desktop drives
-Use parts that consume as little power as possible
-Invest time to figure out how to either build/buy a DC-DC converter, for the power supply, instead of using an inverter, with a standard desktop PSU. Especially if you want to also have a good sound system in your car

I would recommend ripping apart a laptop, and trying to fit the pieces someplace in your car. If the laptops power adapter outputs 12v or so, it should be safe modifying the connector, and wiring it to your battery. I don't know if a laptop has enough tolerance to accept 14.4v, so you might want to use an old laptop that you don't care too much about, if you're going to try this. I would do further research into building something, or looking for a pre-made device that will be able to do this.

The last thing, I would highly recommend looking for a touch screen display. You can probably find a used one pretty cheap on ebay or somewhere. The smaller the display, the better. You should also buy an IR remote

carputers are a great idea but actually putting a desktop pc into the boot of your car will turn out much more expensive then you think, thing is the powersupply in your comp runs on ac, car batteries give out dc so youll need an inverter. also you will need to buy a lcd screen, a cheap lcd is... well cheap but most people have touch screens, theres 2 manufacturers of touch screens suited exactly for the task your thinking of doing but they both retail about 150$. luckily theres a much much better idea.

install a laptop carputer, buy a second hand cheapy pentium 2 laptop, snap the hinges so the lcd flops all the way back and install into your centre console, everythings right there no fucking around, well theres a little, you can either route the power cables directly to the battery (so you can turn it on while the cars off) or connect it to the cigarette lighter hole. and a cool idea is to get the touch pad thats on the other side of the laptop and take it out, still connected place it just below the screen, so when you look at the screen all you see is the lcd and the touch pad, because the rest is behind it.

also final note is all the speakers in the car will need to run off an amp, unless you keep the head unit and connect the laptop speaker cables to the 3.5 jack on your head unit (if you have a newer head unit, old ones wont have it but new ones will for the ipods and such, some could also have a 2.5 but these cables are only like 50 cents from a pc shop)
amps are relatively cheap so buy a 4 way and rig up the 2 4" in the front and the 2 6x9 in the rear (replace the 2 6x9's with 4" front speakers if you have subs too) to the 4 way amp, connect the laptop 3.5 jack to the amp or if it wont fit buy a cable that changes its size, simple as.

Mount this thing in your car:
http://www.axiotron.com/index.php?id=modbook
Peace.

Just take a Mac Mini and a touchscreen panel. Put the computer someplace in the car, mount the screen, and you're basically done.

you could search http://www.mp3car.com
as it sells everything you need for car computing
it sounds like a great idea, im waiting for the wife to let me do it. soon though, very soon
let me know how it comes out if you do it,

sup dawg, we heard you like cars. so we put a car in your car so you can drive while you drive

www.mp3car.com all the way.

Sup, dawg, we heard you like Tokyo Drift, so we replaced your 19" mags with some Chinese plastic spinners and covered your windows with $1 vinyls, so you can look like a playa when you drive!