Both are excellent suggestions. Peter White sells Schwalbe and Nokian studded tires and has an informative page on the different models.

When I bike in the winter, I dress essentially the same way I do for cross-country skiing, except that I wear a helmet. An adjustable balaclava is useful if you're in a stiff wind.

Good lights are essential. I recommend a dynamo hub for reliability, but if you don't want to make the investment, then a headlight with an asymmetric beam such as the Philips Saferide or B&M Ixon IQ allows you to ride safely in the dark without blinding oncoming drivers. The Ixon Pure's beam isn't quite as good but it's still better than the typical symmetric light, which wastes too much light on the ground in front of you and the air above you. The Planet Bike Super Blaze rear light will ensure that you're noticed from behind. Again, Peter White's site has useful information on bicycle lighting.