Cold weather camping is really not that difficult. There is an art, as much as a science, to the whole affair. Make sure your bag is warm enough for you - everyone's thermostat is really different. For good info on products check out REI. You can get some great deals from Northern Mountain Supply and other discount dealers, but you need to know what you want and why.

My experience - Use a ground sheet!

If you want to do extend the comfort range of any bag you can add a liner to make it warmer and wear thermal tops and bottoms and socks to bed. Also be sure and wear something on your head when you sleep, you loose a lot of heat from your head. Use the next day's clothing, if they are clean, as a pillow and put your shoes along with a water bottle in the bottom of your bag to keep everything warm.

The most important thing - STAY DRY! That means venting your tent to keep moisture from breathing from collecting on the roof and raining down on you as frost. If you want to be miserable or worse yet suffer from hypothermia then don't get wet from rain, perspiration or snow. Dress in layers and adjust by taking off or adding layers as you get warm or cold. You can really get in trouble if you allow your clothing to get soaked by perspiration and then stop to setup camp. Also, drink a lot of water - even in the cold. You loose a lot of hydration in cold dry temps. Monitor yourself all the time.

I have spent many comfortable nights in temperatures far lower than what you expect to encounter. The right gear and good planning and execution will make it enjoyable. I lived in a tent in Alaska for a month and a half - 55 to 60 below zero Fahrenheit without wind chill. I have five different sleeping bags and three different pads that can be mixed and matched to the conditions I expect to encounter. Why? Because I hate trying to sleep when I'm cold. It's so nice to crawl into a comfy down or synthetic mummy bag (warmer than rectangle bags due to head covered and less volume for your body to try and heat up) and zoning out. It is good for the soul!