Maybe I should be more specific?

I'm actually not interfacing with the car's ibus, but instead, simulating the ibus enough to operate the screen. All it takes is a pull-up resistor (10K) to twelve volts. I finished the screen wiring this afternoon - used a single Cat 6 cable to run both the video and the "simulated" ibus from the PC in the trunk. The LCD itself is a 6.5" but it requires RGsB at NTSC or PAL timings. I use an old Matrox G200 and Powerstrip to generate the right signal. Mostly since the G200 will also output the required Sync on Green natively. As for data packets there are only a few relevant ones. First, the monitor needs 80 xx bf 11 01 xx - which is a general bus-wide wakeup (key on). Then you can use 3b xx f0 4f 11 11 xx and 3b xx f0 4f 01 01 xx to turn the video on and off respectively. The monitor also needs a keep alive packet sent every 18-20 seconds - 3b xx 46 01 xx. I send it every 10 or so just to be safe - the count resets everytime it receives the message. And finally, to turn the monitor off, send 80 xx bf 11 00 xx (key off). For those who arent' familiar the packets are structured like so:

aa bb cc yy yy yy yy yy xx

aa - sending device address
bb - total packet length
cc - receiving device address
yy - data
xx - checksum