BMW 525d 2006 front screen interface

I am fitting dvd, digital freeview tv and two rear headrest monitors in 2006 model BMW 525d, the car has factory fitted front screen/sat nav./radio/cd player, i am going to link into the auxilliary sound circuit (rear 3.5mm stereo jack) on this system to put sound through the factory speakers, does anyone know how to link into the system to put the picture on the front screen when stationery ?, does this have to be done with an expensive interface box ?, if so where is the best place to buy one ?, will this cause any problems with the factory system? All the equipment I am using is basic stuff i.e connected with phono leads.

Many Thanks !

if the nav box (were the disk goes)is separate from the screen you can use a universal vci-x interface from pac it will require you to find the RGB wires,  thay have no suport for BMW's  http://pac-audio.com/products/productsCatagory.asp?mmSearch=Audio%20Video%20Accessories

usa spec also has a non universal one its new to me i just found about it today not sure how plug and play it is or of the full applications i just orderd one for an X3 and will try it next week http://usaspec.com/index.html  thay dont have any of the video interfaces on the web site but you can call for applications 

Hi mcgrath809.

We have an interface for this car and many other. Visit us at www.TVandNav2Go.com

Thanks Dominic