In response to the original poster, snow tires are indeed absolutely necessary if you ever plan on driving an M3 in any kind of snow or freezing rain. I tried to drive my sedan in about 1 inch of snow once and was blown away at how unstable the car was with the summer performance tires. I basically had to turn the car around and park it.
I picked up a set of OEM 18s from a fellow poster with like 30 miles on the tires (he pulled the OEM rims and tires off immediately after driving his new M3 home from the dealer as he was putting an aftermarket set of 19s on) and then bought a set of Pirelli Sottozeros from TireRack. The Pirellis fit perfectly on the stock 18s, and they drive pretty nicely even without snow. With the Pirellis, the M3 feels slightly more stable in snow and slush than my old 330 with all seasons. HUGE difference.
In any event, I may be selling my M3 shortly and thus looking to offload the 18s, the Pirellis, and the set of stock Michellin PS2s I pulled off the 18s. I'll post in a week or so if I decide to do it.
My advice is to not drive your new M in any kind of snow without proper winter tires or, at a minimum, all season PS2s.