Snow and Ice. It's the great equalizer for a day. The white blanket evens out dips and rises in the landscape, and creates a sense of equality to a scene.
It's also a pain in the butt to shoot in. Your camera is a simple instrument, even for the $8,000 Nikon D3x. They're all just a light tight box made for capturing an image. In snow, most camera meters will underexpose. They see the mass of white in front of them, and they try to make the scene 18% grey. It's not the meter's fault; it's what it is designed to do. With traditional centerweighted or spot meters, you need to over expose by about 2 stops - i.e. go from 1/1000th of a second to 1/250th of a second for a shutter speed. My Nikons are a bit better with their matrix metering - I usually only need to adjust about a stop to get my whites white again.
Your best bet in this type of situation is to bracket the shot - i.e. take a photo at your best guess exposure, a stop above and a stop below. With digital, you can check the histogram afterwards and see which one looks best. You want to make sure you haven't clipped any important highlight areas, or lost a lot of shadow detail.
Street photography gets a bit tough in the winter; people tend to hunker down inside during storms, and in the cold weather. Your options become a bit more limited. But there's always someone out having fun.
Embrace the cold though, and go get some shots. It's a fun world in the snow. I find that I tend to shoot more black and white in the winter, the starkness of the atmosphere seems to call for it. But if you can find it, the juxtaposition of color in the shades of gray of a winter day can make a shot really stand out.
Take Care for now, and enjoy the rest of winter! Mud Season (some like to call it spring I'm told) brings its own joys to photography.