Microsoft is talking up the energy-saving aspects of its new, oh-so-long-in-the-making Vista operating system -- namely, that it's good at putting computers to sleep. On the other hand, Vista's fancy-schmancy 3-D interface sucks up a fair bit of juice. Also, most existing computers aren't powerful enough to run the system, which has some enviros worried that Vista could prompt a big new wave of electronic waste as people dump their old machines and buy spiffy new ones. Has Microsoft really earned its green bragging rights? Kate Galbraith investigates.