There are ways to tap into the factory screen. I did alot of research on this last year, but gave up cause I could not find a screen. There is a lot of cool stuff you can do with a carputer especially in a BMW with ibus, as everything is run of codes (IIRC it is HEX or something). If you want to do this, do alot of research.
www.mp3car.com is a good way to find information on this. You can run GPS, MP3, movies, Bluetooth phone all off the carputer.
This guy took a Z4 Screen and a carputer and put it in his 540i.
http://web.mac.com/jlitko/iWeb/BMW%2...5E0706921.html
http://www.mp3car.com/vbulletin/work...-part-2-a.html
http://web.mac.com/jlitko/iWeb/BMW%2...0Part%202.html
http://www.bimmerboard.com/forums/posts/142176