You can do either/or. Dynamic flexibility (stretching) kills two birds with one stone as you'll be stretching whilst warming up. It can be done from cold but start small & look to increase the range of motion per exercise over several reps.
Even if I had any plans to chicken out of the VLM, there's no way I'm backing out now. The actions of the idiots behind the Boston explosions makes me even more determined to take part. If they cancel the event I'll go & run the course anyway
It's a tricky one!!! Treadmills can be useful but don't have downhills, bends, t-junctions, potholes, dog poo etc. However at this late stage (before the marathon) you also need an injury like a hole in the head, therefore the treadmill may be a wiser option.
If you prefer to run outside it may be better to go somewhere where the snow lays evenly (e.g. a park/playing field), doing multiple laps and, as others have pointed out, running for time rather than distance.
Visit www.theisrm.com or www.thesma.org both will have a "therapists directory/find a practitioner" search facility for a well qualified sports massage practitioner who is likely to be more specialised and cheaper than a physio