In reply to south west stew: Hey Stew, I''l fly in the face of some of the comments. I would go straight to a B3 (I actually did) if you think you will be very serious about getting into winter climbing and walking for that matter.
I have only been winter climbing for a few years now, but went straight for the B3 due to cost. They are more expensive, but I knew I was going to like it and get hooked, so ultimately saved money. I shopped around and purchased something was confortable for me at the time (Scarpa Freney XT) and have had several years of great winter/ice climbing and alpine trips out of them.
The link to AK's article is a great source of info for crampons.
Good luck and be safe.
S