In order to watch HD movies, the source of your content must be HD. Currently I am using the DVD to watch the content. I would normally put on MTVs while driving, but if my little one is in the car, I will just put a cartoon or something for him.
Alternately, you can buy an optional BMW double screen to be placed behind the front seats which is hooked to the iDrive.
To be able to watch multimedia/ streaming content, I believe you have to attach your iPhone to the optional Snap-in-Adapter. There are 3 versions that look alike, so you need to get the "Media" version, which is the most expensive one. (I didn't buy one yet, but I was told.)
To be able to connect streaming contents and listen to the global network channels in Asia, North America, South America, Europe, Middle East, Australia and even Africa, you need to download various apps from the AppStore. The application must have 3G connection and attached to your car with a good signal. A stronger signal is received if you use the Snap-in-Adaptor (any version) because it is directly using the vehicle's built-in antenna.
If you have a AppStore Account registered in US/Europe, you will be able to access many cool free/paid apps for your BMW F10s/F30s only.
That's all I know so far, and still exploring. Hope this helps.