Well, I've never lived in Wisconsin, but I've cycled all winter in snow and ice. You just need to be prepared. You definitely need to be visible--obnoxiously so. Don't get all self-conscious about wearing screamin' yellow--lots of it!

You'll also need lights: good headlamps are expensive but worth it. And tail a tail light or two. And reflector ankle bands.

You'll also need to keep warm! Layers! I love using old cashmere sweater as a layer when it's really cold. Also two pairs of socks (one wicking, one wool) and shoe covers if I'll be out long. Good warm hiking boots work well if you don't have clipless pedals. Keep your head warm and the rest of you will stay warm, too. Get a thin skullcap for under your helmet--or a balacava if it's really cold. As for gloves, I love my Pearl Izumi lobster gloves. Other folks have other gloves that they really like.

I commuted all through the winter in Washington DC when I lived there. Mind you, it doesn't get so cold as Wisconsin, and I didn't ride when it was below 20F. I did ride down to 20F and in the ice and snow. The bike trails there don't get shoveled, so the snow turns to ice and stays. I had an ice bike for those days--with studded tires. Practice before you go out in traffic in the snow and ice.

I loved my winter commute--the only thing that kept me off was darkness, so I chose to ride to work in the morning and take the Metro home in the evening, with my bike. It made for a very long day sometimes, but I did end up getting a folding bike that allowed me to use the Metro earlier than 7pm.

Best of luck and enjoy the winter!

EDIT: check out www.icebike.org