The service manual calls for the radiator to be removed and the coolant tank disengaged, per the pics below. Obviously the first step is to remove the radiator cover.
Sorry for the poor image quality. Pics are from a cell phone off a laptop running the DVD of the service manual, which is the only way you can get it. A dealer service tech told me a few weeks ago they can't even get printed copies from BMW.
Here's the technical info:
Spark Plugs: NGK LMAR8D-J.
BMW Spark Plug Socket: BMW Part # 83 30 0 495 560 ($42.25 online).
BMW Ignition Coil Puller: BMW Part # 83 30 2 153 002 ($53.05 online ... or, you know, use your fingers ;o).
TORQUE spark plug: 12 Nm (9 ft. lbs.).
GAP spark plug: 0.7 to 0.9 mm.
I believe BMW calls for replacing plugs every 7.5k, but I'm sure 10k would be fine.