One of Microsoft's labs created a video on measuring power consumption on desktop devices. This video is appropriate for someone who is new to measuring energy consumption on the desktop.

So how much power do your PCs draw? And how do you figure that out?
Those were the questions that I asked Grant after he recently updated the machines in some of the classrooms he manages. His problem was even more complex: He needed stronger/better/faster machines, but he was at capacity on his circuits, so he needed to do it without increasing power draw.
In this video, Grant walks us through some of his methodology in measuring and benchmarking power consumption on a few machines, and shares the results with us.
It leads to some interesting conclusions, and some good food for thought for anyone trying to make energy conscious decisions around PC purchases.

In this video they use the Watt's up device, but hopefully, they'll put the Smart Watt device in their small server room.