I used BlueMagic to clean up the chrome on my old Harley. Haven't tried it on the Bimmer trim, but can vouch worked great on the bike.
http://www.amazon.com/BlueMagic-400-.../dp/B000BO8Z9I
The chrome trim on my E46 is still in good shape, I use Nevr-Dull to take off the water marks, and give a little shine
http://www.autogeek.net/eo104.html