What is the environmental impact of PC gaming?

I just read this article http://abcnews.go.com/Technology/GlobalWarming/story?id=7343518&page=1 about the carbon footprint of spam emails. This makes me wonder...if sending emails can waste so much energy, how much energy does my computer use when playing a computer game? I have noticed that when I play a game on my laptop the battery life decreases by a factor of 3 (and my laptop heats up to like a bazillion degrees). Am I harming the environment when I play a game? How does computer use compare to driving a car?