For anyone interested in winter hiking I would highly recommend the AMC Winter Hiking Workshop. I attended the course a few years ago and again this year as a refresher. The instruction and reference materials are excelent. Unfortunately, the course offered by the Boston Chapter for winter 2006/2007 is already completed. But you might check with other chapters (NH?). They have similar workshops at different times.
The course I took through the Boston Chapter was very inexpensive ($35 and we met every Tuesday evening for five weeks) and very informative.