Now, Microsoft has launched a determined counteroffensive. Its uncharacteristically cool TV ads emphasize the affordability of PCs vs. Macs. And it has started offering PC makers a version of Windows, normally around $70, for as little as $15. Mac sales are sliding, and Linux is disappearing from most netbooks. Researcher NPD says 95% of PCs with a small screen and a sub-$500 price tag run Windows today, up from 10% in early 2008. "Microsoft has driven Linux off the lot in netbooks," says Roger Kay, founder of tech research firm Endpoint Technologies Associates.