I'm now fully media capable
I can carry my entire cd collection and video collection with me and access the internet when needed.
Cartop

mouse and keyboard

media player (Frodoplayer)

visuals instead of boring disclaimer type crap

install location

windows screen shot to show clarity of OEM NAV screen

just another screen shot of the media player (Frodoplayer)

Reverse camera (the 04’s didn’t come with this option)

DVD w/TV tuner as a second source
And I have on input left for a future video game player.....shhhh don't tell the Wife, I said I was done messing around with the system.
edit: I'll try and give you all a quick run down of my setup, if I missed a question or didn't answer a question specifically feel free to ask again.
I have the factory navigation system so I bought a switcher box from Avelectronics.com. The box is great because I can switch between any 4 inputs and put them on any of up to 4 screens with a different or same source on any of them. Sam the owner is also a great guy to work with. It's fairly easy to install just need to cut 4 wires but the place to cut in is behind the monitor so you have to pull the dash apart some. I have the rear video audio going to the factory DVD wiring and the front audio going to the AUX jack (all from the box through P.I.E. amps). This allows the front to watch either the DVD or PC and listen over the cabin speakers while the rear uses headphones and can watch/listen to any source. ALL of the fatory nav still works. I flip a switch to toggle between my av screen and factory screen which does not affect the nav at all so it can still be shouting direction to you as you are listening to mp3's. The connection is just to the monitor so there is nothing with the vehicle monitoring systems affected.
The factory screen is actually very good. If I didn't have it though I would get a VGA screen. It seems that most people are using the Xenarc or Lillput screens. I don't think I'd use a touch screen though. It's a fairly far reach and you really don't need to do much once you get the player playing etc. I have hotkeys set up on the keyboard so all I have to do is hit a button for next song etc. A good site with great prices but not so much name brand is webzone.com which you might want to check out even if just for DVD.
I started out wanting just a mp3 player with a video interface but what crappy things there are out there the cost was close to that of a full blown pc which you can do A LOT more with, so that’s how I ended up with the PC. I did find this thing though that would be nice but I got tired of waiting for it to come out and not knowing the price I bit the bullet and order the PC.
http://www.airlinktek.com/english/prod_mg350.htm
The PC I bought from logicsupply.com. I bought the case, hard drive, motherboard, ram and power supply from them. The case is the Morex 3688, the motherboard is Epia MII12000 (1.2ghz), Ram is 512mb and the power supply is the M1-ATX and a 40gig hard rive. I did the assembly myself which after the fact wasn't so bad but if I didn't have some IT help at work I'd of thought the $35 assembly was cheap. I picked up a slim CD drive for $10 off the internet somewhere. This is not a powerhouse PC. The big thing with car PC's is that you normally don't have a need for something that can run the newest video game with the high 3d graphics so a P4 is often overkill and they are power hungry and run a lot hotter. The power supply controller is a must have, it keeps the voltage constant and allows the pc to survive engine cranking and will shut everything down if it senses the battery is getting low or the PC is overheating.
I took and made a connector between the AC/DC power brick and the wires going to the power supply. This way I can just unhook from the car and then take the pc inside and hook it up in there.
When you run cables you will want to run 2 usb and 1 firewire. I've learned that if you hook 1 usb 1.0 device up then everything on that line will be 1.0 even if it is a 2.0 device...now having said that I guess I haven't checked to see if it makes things hooked to the other usb cable 1.0 as well. But the mini keyboard and mouse I'm using are 1.0 and I have an 80gig portable 2.5" drive that has firewire and usb. The portable is nice because it makes it easy to take media off the home PC and move it to the car. With a 2.5" disk it will self power off of the USB or Firewire so just plug and play. I doubt I'll add a DVD player to the PC as I already have one in the center console so everything on a disk (prior to me converting it to Divx) will be played through there. But if I did I'd get a slim usb slot load.
I bought my cables from mwave.com they were about the best prices and they ship fast.
I put a couple 92mm cooling fans in the floor compartment where I have the pc installed. One sucks the other blows...literally I had to but a couple empty water bottles under the third row seats to hold the short carpet skirt up so the air can circulate. After I did that the PC seems to be running fairly cool in the floor compartment. Before I got the skirt out of the way the case was getting pretty hot to the touch.
Now I suggest going to Mp3car.com and reading through the forums over there. It's a little overwhelming at first and it seems to be mostly a very young crowd so sometime the manners suffer especially if it's asking a question that has been asked often. The site is VERY active as it is world wide so there are easily 300 post a day. I spent probably 6 weeks reading before I bought my equipment and then have been over there almost everyday trying to tweak the system and trouble shoot....and I've found 99% of the questions I had just searching.
I was using the hibernate feature which took about 30 seconds to come up once I turned on the key but I am now trying out the standby which gives me about 5 seconds to come back after the key is turned on. The standby uses more power though so I will keep and eye on the battery but like I said before the power supply controller is suppose to shut everything down if the battery drops below a certain voltage for more than 1 minute.
I can connect to my home network setting in the driveway but only with the floor space open is it reliable. I have an elcheapo usb wifi on it now. I'm going to get something different with and antenna that I can move out of the floor compartment and put in the rear drivers side compartment. The other thing I will be doing is getting an usb sync cable for the cell phone. I can then use it as a modem...though the carrier frowns on this, as they want you to buy their dedicated wifi card..but I won't be using it but occasionally. This will allow me to at any time and place (practically) connect to the internet to look up a number or address...or kill time surfing in the local mall parking lot waiting on the wife...that is until football season starts then I'll be sitting in the parking lot watching the game....I may also add a cheap laptop type gps software. My parents have one that allows you to log onto a web site and tract someone if they have an internet connection every so often to upload their coordinates. Thought that would be cool when we go on a long trip and our destination can see just how far out we are....though its just as easy to call I guess...just not as geek
I'll help answer as many question as I can but I'm by no means a PC expert.