Today I ran into an article about Microsoft's join effort with a Seattle-based start-up company, Verdiem campaigning the energy-saving opportunity in PCs by distributing a free software tool, named Edison to help customers saving the energy. Very good initiative indeed! I've downloaded and installed the software to my PC, it allows me to estimate how much energy could be saved by adjusting the PC's power consumption settings (i.e. put display or disk to sleep mode, etc.) through the app. It works pretty well for me, so you may want to give it a try. Also, check out this nice blog from Microsoft's Environmental Sustainability team.