FYI, for anyone so inclined. I poked around on the can bus a long time ago with some help from someone else. I was able to display custom text on the stock head unit. Don't get your hopes up you have to switch modes out of playing the cd to display the text, so reading the id3 of an mp3 and playing track/artist info nearly impossible to do...

the following can bus info is helpful for other reasons though:

the website is called hack a day dot com

CAN Hacking
Introductions
The In-vehicle Network
CAN Protocols
Building CAN Hardware

(Don't be afraid, it's not a hackers site its a site that engineers and tinkerers explore modifying things for other uses. Some pretty cool products and things are out there, like how to take a $1,000 flir camera and make it a $6,000 flir camera just by tweaking the files. fun and silly things also.)

 

Also try hacktheibus yahoo group, BMWcoding forum; the E46fanatics subforum for electronics; the forum for the IntraveeII (bimmerforums or x5bimmers I think)and xoutput electronics sub forum.

And it's a LIN bus not a CAN bus. The canbus is reserved for mission-critical high speed balanced comms between the EMS, DSC and EGS.