How do I prepare for winter bicycling- myself, my bike...?

I use my bike to get to and from work and I'm looking at having to do so this winter. What do I need for myself and my bike to survive this (don't say a car)?
I'll have to take into account the darkness, the cold, and the precipitation. I will be riding part street and part mostly flat trail. The bike I'm going to use has a hardtail moutain bike frame and hybrid tires.

thanks for any help/advice.
It is about a seven mile ride on road/ trail half/half. The trail part used to be railroad tracks so it is pretty flat. The ride takes about 40 minutes in the summer.