I agree with Aaron. You definitely need 4 snow and ice tires installed. I know it's an expense, but believe me, after you get them, you won't believe you got by without them. (Come to think of it, you are not getting by now!)
I bought a set of Artic Alpins for my wife's car this year and they make a big, big difference over the all season tires that they replaced.
I have also used snow and ice tires for years with my Audi Quattro. Even with an AWD car, they make a difference. Remember, your tires are your only four contact points with the road.