Not to sound repetitive, but the key is a good set of snow tires (all fours, not just the rears). Then, put a couple of heavy bags of sand, salt, whatever in the trunk (one over each wheel) and you will feel invincible. In my old three series I was able to easily plow through snow over a foot deep without a second thought.

The reason you need snows on the front as well as on your drive wheels is for steering and braking. Without them, you'll have an uncontrollable toboggan.