Green Operating System?

“The system (Windows Vista) that has been blamed, it seems, for everything from global warming to the U.S. economic meltdown.” PCWorld

Is there any connection between OS and global warming? Ooo...may be with the software to calculate the impact of desktop/laptop PC to our world. But must people use Mac OS X Leopard rather then Windows Vista. Is there any analysis from the Greenpeace which OS is friendlier to environment?