What sort of snow conditions are you running in? For dry, powdery snow, the best option is a pair running shoes that have aggressive tread (search for "trail running shoes"), but in wet, icy snow, metal screws or spikes will give you the extra grip you're looking for. I can't think of anything that will help more than it will hurt on icy pavement other than proceeding with caution.
You should be aware that traction devices have their own limitations. Metal spikes or screws will severely reduce the amount of traction you get on cleared pavement. On bare pavement or hard ice, the metal screw technique Sarge mentioned also has the potential to cause blisters and irritation just like using XC spikes on pavement does. If you need the traction devices for only a short portion of your run, you will be better off just being careful on the slippery parts. That seems to be the approach a vast majority of competitive runners take, even in severe winters in Minnesota.