The analyst firm believes that businesses can achieve substantially the same improvements offered by Vista's energy saving features by educating users to use existing Windows XP PCs more effectively.
Instead of rolling out Vista, firms are advised that they can spend a much smaller amount on a broad-based education and training programme to help staff understand why saving energy is important to the business.
"Vista's power management improvements are useful but limited. Similar energy cuts can be made with XP-based systems by changing user behaviour like shutting down PCs after hours," said a Gartner report written by research vice president Simon Mingay.
The warning follows Microsoft's recent claims that power management features in Vista could help a business with 200 PCs to reduce carbon dioxide emissions by 45 tons a year.
Improved features include better power management, and more stringent default power-saving settings.
Gartner welcomed any efforts to reduce the carbon footprint of computers. The firm estimates that PCs account for more than 0.5 per cent of global carbon dioxide emissions and represent a "significant proportion" of office electricity bills.
"Although Vista's power management technology is helpful, a comprehensive energy-saving programme requires addressing people and process issues as well," Mingay stated.
"In fact, just about the same savings in electricity and carbon dioxide emissions can be made with XP-based systems through user education and motivation, and by making the best use of existing XP power management features. "
Gartner's examples of what firms should do to improve energy efficiency include:
- Shutting PCs down after hours
- Eliminating active screen savers
- Ensuring monitors switch to standby after 10 minutes of inactivity
"Our research shows that most users respond very positively when education and behavioural changes are part of a broad programme to save energy and cut carbon dioxide emissions," said Mingay.
"People and process changes are harder to make than technology changes, but they go much deeper and will have an impact beyond any Windows upgrade.
"Businesses should not justify upgrading to Vista just because of improved power management. But Vista's features will help where users do not cooperate."