Help with in-car computer.

Hey guys.
Alright. I'm throwing a computer in my trunk that I've made out of leftovers. Surprisingly, I've got some decent stuff going into this build. But before this goes anywhere, I have a few questions (which may be stupid.)

1: I've been looking for a 2-DIN in-dash monitor that isn't touchscreen or has navigation or a DVD player... any help? I had plans for an external drive to be hooked up when necessary via a long USB cable. Also, I see these screens with buttons all over the front of them and I'm wondering if I hook it up to run as a monitor will those function buttons work?
2: How do I go from my stock speakers (for now) to my on-board Realtek 5.1 sound (again, for now)? Do I have to go through an amplifier to go from the speakers to an audio cable that the computer would use? Is there any conversion necessary? Sorry, I've never seen car audio before in my life.

Thats all I can think of for now. Any help would be greatly appreciated!

Here's the **** laying on my bedroom floor. Sorry about the poor quality picture. I'll take better ones when more is finalized.

Just so you guys know, after I have these questions answered and some money in my pocket, this project's going to be completed.

System spec's:
Micro-ATX Motherboard w/ on-board nVidia 6-series graphics & on-board Realtek 5.1 Sound (For now. Looking to upgrade to a stand-alone sound card.)
AMD 1.6GHz Sempron socket 754
1GB DDR 233
32GB IDE hard disk (For now. Looking to upgrade to a +60GB SATA laptop HD.)
305W power supply
Running Windows XP Media Center Edition.

I'm hoping to power this thing with a power inverter. Any comments on my abnility (or lack thereof) to do so would also be helpful.)

Thanks.

before i try this, ill say ive never done this. my advice is free, so take it as such

Q1: Aren't there ebay monitors or headrest monitors that don't have any of that stuff? I think the buttons would just function within the monitor menus, like selecting input source and such.
Q2: from what ive read, people are split on what you can run off a sound card. some say you can be ok with a cheap creative usb like mine that has RCA outs. other say you need a pro $300+ card whose brand starts with M...google "sound card rca" or something like that...should come up with it. im too tired to do it now and yes, to run off RCA outs you would need an amp.

that inverter is going to have to be largeeeeeee...theres a reason why people use itx boards and psu's in the car. ive seen carputers with regular atx psu's before, but dont know what inverter they were running off of.

ugh thats all my brain can come up with now...

check out http://www.mp3car.com im sure you will find what your looking for on their forum.... since thats basically all it is. lol

MP3Car is probably the bast way to go, though I don't have any direct experience. I know I've seen a few people using a sound card with a toslink out and sending it to a digital processor, but you will start to get into a lot of money quickly!!!

Thanks for the help thusfar.
I'm looking into all of the above mentioned information.
I'm confident I can use the majority of my current setup and get this thing going for a small amount of cash.
...we'll see what happens =]