If you don't mind the use of root, the following will give you the ability to throttle cpu frequency which could result in reducing power consumption. Note that Hardy defaults CPU frequency throttling to 'ondemand'. First do this:
Originally Posted by wilbur.harvey
Then add the CPU frequency scaling monitor applet to your Gnome Panel. This will let you run the applet as root which will give you left click access to manually changing the CPU performance profile. You can add an applet for each processor you have, selecting it in the preferences.
sudo dpkg-reconfigure gnome-applets