yea, the best way to deal w/ driving an m in the snow is to have a spare winter ride
for those that don't have one, yea def buy either steel rims from your bmw dealer, or where ever, or cheap but descent looking rims, and set of winters to go w/ em.
i was going to buy the dunlop m3s, they were rated pretty good by the tirerack, along w/ refurbed 10 spoke m rims found on the 330 sport package, but couldn't find any around the area. long story, but i just got access to my older talon, so i'm just gonna drive that aroudn in the winter.
btw, get all 4 snows the same size and width, so you can rotate them for next year to eek out maybe one more season, extending the life of the snows to maybe 4 or 5 winters..