When you unplug your system, it will automatically dim the screen slightly, reduce the clock speed of the processor, and turn the screen and hard drive off if you don't use the system after a certain amount of time. Whether you use Windows or a Mac, be sure to take advantage of the power management options in your system to control these options to turn off devices and components automatically. In Windows you can use the Power Options control panel, but if the manufacturer supplies a power utility, it will likely give you control of more devices.

You can create multiple power profiles in Windows XP, to let you dim the screen further, set the processor to a higher speed for performance or a lower speed for better battery life, turn off Wi-Fi and network connections, or spin the hard drive down more quickly. These will all save power if you don't need the associated features.

Another idea is to tune the system settings to give you longer battery life when you're playing DVDs. Dim the screen as much as you can, as it uses more power than almost any other component in the system. You can see the difference in the battery estimate in the Windows taskbar; you could gain as much as an extra hour of battery life.

While you're at it, set your PC to hibernate when you shut the lid rather than going into suspend mode. This saves the contents of memory to the hard drive and shuts the system down completely, so it uses nearly no power. Even better, if the power does run out, you'll be able to carry on working when you plug in again.