Iphone 3GS AV Composite cable

[staffop]

I'm after a cable which is compatible with the new Iphone 3GS that has the dock connector on one end and composite Audio/Video (RCA) connectors on the other. I'm planning to use it in the X5 for the TV screens in the back so the cable would need to be quite long and preferably be able to charge the Iphone as well.
I've heard that Apple use authentication chips in their genuine cables which surpress messages on the newer iphone/Ipods about compatibility - anyone come across this?

[sdsurfer]

I used this with 3GS for 2 month before I changed my navigation unit .
Pac-Audio.com Product Details | iPod Integration for your car and More by Pac-Audio - Connecting you to the future

It worked flawlessly without any pop out message.