Getting winter tyres can a good idea, but it is a big expense and a lot of hassle. Ideally you would have 2 sets of wheels, 1 with summer tyres, the other with winter. If you can afford to, and have some means to change them over relatively easily, then yes absolutely. If not, I would say use wet weather tyres (like me, uniroyals), which given the climate these days, are certainly going to earn their keep!, and they will work better in the snow than summer tyres. but I don't see winter tyres as being necessary, drive carefully plan well ahead, leave a very big gap in between you and whatever is in front of you, use the gears to help slow you down, and don't make any sudden manoeuvres. One thing I definitely wouldn't do is buy cheap tyres, that is a very false economy.
I am also utterly baffled by dannymack's comment on letting the tyres down a little. I am assuming you mean pressure?, but why on earth would you do that?. If it is snowing, you want your tyres to cut down through the snow to find the grip, not float over the top providing no grip at all!. Yes if you are in Iceland or somewhere, driving on very deep snow, you let the tyre pressures down for floatation, same for deep mud. Doing it on the road could be very dangerous.