Over the last five years we have cut our energy consumption by over half without sacrificing a huge lifestyle change.  Our appliances are more energy efficient, we moved into a smaller house, we eat practically no meat, and our transportation has been supplimented by an electric bike for running local errands.  
Here's a link which measures your earth footprint. 
 http://www.earthday.net/footprint/index.asp   
Just taking small steps at first like checking the tire pressure on tires and driving slower on the hiway is how we started.  Then we changed all the lightbulbs in our house to fluorescent and paid more attention to shutting off electrical appliances when not in use.  
We found that conserving energy and therefore reducing CO2 output was easier than we first thought.  The next challenge we face, is cutting our energy consumption by another 50 percent.  We've made it into a game which we enjoy playing.  We look at it as doing something beneficial for our children's future.