Linux vs. Windows Power Usage
 

Since publishing our Ubuntu power tests, where we had
monitored the power consumption of the past six Ubuntu releases going
back two years on a laptop, we've had repeated requests for a power
comparison between Windows and different Linux distributions. Well, in
this article are the first set of results from that testing. We've
compared the power consumption of Microsoft Windows XP, Windows Vista,
Fedora 7, and Ubuntu 7.10.

http://www.phoronix.com/vr.php?view=11248