I've read all your posts, and I like all the information you've given. I wanted to update you guys on how things are proceeding.
It turns out that the ECU (the computer in the car) can output either CAN or serial, but not both. It already has to output CAN for something else, so I'll be tapping into that. My new plan is to run an Arduino Uno R3 with a CAN shield to get all the information (there is somebody else here that has done this before, so I'm not getting in too far over my head). It will do the processing required to convert the CAN inputs into something a little easier to handle, and then it will send this information to an Arduino Pro Mini that is connected serially with the screen. If the CAN shield doesn't interfere with the Uno's serial pins, I may drop the Pro Mini entirely.
Sacman, I tried interfacing with the screen in SGC mode, but I was having a lot of trouble. Installing the libraries and running the sample code only gave me errors (I had to download and rename some additional files, and even then it wouldn't work). I'll be running the screen in GFX mode; it will handle the displaying of all the text and images, and the Arduino(s) will just handle translating the CAN signal into values to pass to the screen. I haven't hooked the Arduino and screen together yet, but both of them are interfacing as expected when connected to a computer.
Hopefully I'll be able to post a video when it's finished. I think it'll be pretty cool.