Getting correctly exposed pictures of the snow can be a tricky thing to do. I'm writing this article to help make your life easier.
When shooting in the snow, your camera will have a difficult time getting the exposure correct, as it doesn't see the snow as being white, but it actually thinks it's grey. You have to adjust your camera to compensate for this. Most (if not all) modern DSLR camera's will have a feature called "Exposure Compensation". You can see the function button on my camera. It is the button that is to the left of the ISO button. Also in the display (top right corner of the display) shows how much compensation is being used. In this particular case, the compensation is +2.0 units (stops). My camera will also show you on the back LCD screen how much compensation is being used. Also in my case, the top screen only shows up to + or - 2.0 stops, but the back display will actually show + or - 5.0 stops. (full range on my camera)
When shooting in the snow, the amount you apply will depend on the conditions you're shooting in, but I recommend starting at +1.5 and adjust from there. Using the histogram on your camera will help you out a lot. Have a look at the 2 samples I've posted below. The first one is the histogram of snow with no exposure compensation and the second one is with 2 stops of compensation. You might be thinking that you've been told in the past that you want your peaks to be in the middle, but as mentioned earlier, if it's in the middle, then the camera sees your white as being grey. If you want your white to actually be white, then you'll want the peaks to be just to the left of the right side of the histogram. If you get too close to the right hand side, you're whites will get blown out and you may not be able to recover them.
As a note, I shoot primarily in aperture priority mode and shutter priority mode, and this technique works well in these modes. I have never shot in full automatic mode, but the procedure should work in any of these automatic or semi automatic modes. If you're shooting in manual mode, typically exposure compensation won't work, but I have heard that in some camera's it does, so if you're trying this procedure in manual mode and it doesn't work, this would be why.
To achieve the same results in manual mode, start with setting your exposure to zero using your viewfinder or LCD. To replicate a +2.0, adjust your exposure so it's showing in your viewfinder or LCD as being overexposed by +2.0 stops. If your camera is set in 1/3 stop increments (by default it probably is), then you can adjust your aperture or shutter speed by 6 clicks of your e-dial. (3 clicks = 1 stop) Just make sure you're adjusting so your meter is on the plus side.
I hope this tutorial helps you get better snow pictures. If you do have any questions, please don't hesitate to drop me an e-mail and I'll see what I can do to answer your questions.