A laptop consumes fives times less energy than a desktop PC. You can easily find models with powerful feature sets that easily stand up to those Desktop Counterparts. In fact, most laptops include options for dual-core processors, and some find enough space for two video cards in a Scalable Link Interface (SLI) configuration, perfect for those all-night fragging sessions.

The monitor, chances are you'll buy a flat-panel display since most vendors have stopped selling Large Sized CRTs. An LCD uses about one-third the power required to run a CRT.  A 19-inch LCD consumes an average of 45 watts, and 100 watts for a 19-inch CRT.

It's pretty simple to set up the power-saving options in Windows. Power consumption in Windows Vista is more adjustable than in Windows XP. Vista can adjust its performance to fit the task you're working on, boosting processing power when you're watching or editing a video, then lowering it when you're just tapping out a document.

An initiative launched by utility companies and energy-efficiency organizations has resulted in real-world energy-saving PSUs. The voluntary certification program, known as the 80 Plus program, aims to make power supplies at least 80 percent energy-efficient. And because these energy-efficient PSUs aren't overindulging on heat-generating energy, they can also eliminate the need for a fan, resulting in a quieter, more-reliable PC. Approximately 100 designs from almost 25 manufacturers now bear the 80 Plus label.

Designers of processors have been working to reduce power draw for years now. The Intel Core 2 Duo desktop processor is up to 40 percent faster and more than 40 percent more energy-efficient than its single-core predecessor. It optimizes power consumption by powering up processor components only when necessary.

Intel claims that its Centrino Duo laptop technology is twice as fast as previous versions, yet consumes 28 percent less power. Also very efficient are Intel's Pentium M and Celeron M processors and AMD's Turion 64 and dual-core Turion 64 X2.

Video cards remain energy hogs. High-end cards easily exceed 100 watts at full load, and popular dual-card setups for gaming double that wattage. Choosing a graphics card that fits your needs is key. If you don't play advanced 3D games, go with integrated graphics for the lowest power consumption.

Electronic Product Environmental Assessment Tool (EPEAT). EPEAT is a system to help evaluate, compare and select desktop computers, notebooks and monitors based on their environmental attributes.

In Europe, RoHS-compliant products intentionally exclude specific hazardous substances such as lead, mercury, hexavalent chromium, cadmium, and some brominated flame retardants.

The U.S. Environmental Protection Agency (EPA) estimates that purchases of EPEAT-registered PCs over the next five years will reduce hazardous waste by more than 4 million pounds (the equivalent of 266 elephants), eliminate more than 1 million pounds (66 of those pachyderms) of nonhazardous waste, and save more than 200,000 megawatt hours of energy—enough to power 2 million homes.

You must evaluate a prospective PC's overall energy consumption by finding out how much electricity it draws when idle and at full power. A desktop that uses 4 watts or less when in sleep mode, and 50 watts or less when idle; For laptops, the ideal is 2 watts or less in sleep mode, and 14 to 22 watts (or even less) in idle mode, depending on the graphics configuration.