Vista was being used on less than 1 percent of PCs tracked in February by Aliso Viejo-based Net Applications Inc., making it the sixth most-popular operating system. That puts it behind Windows 98, which is still used on 1.5 percent of computers.

Vista's exact share was 0.93 percent. Windows XP continued to lead, with 84.3 percent, followed by Windows 2000, with 4.8 percent. Mac OS X on PowerPC machines had 4.3 percent, while newer Intel-based PCs running OS X had 2.1 percent.

Net Applications collects its data from the browsers of visitors to its network of more than 40,000 Web sites.

Vista's February share of PCs connected to the Internet -- a month after its consumer release and three months after its release to businesses -- represents a big leap over January, when it was used by just 0.2 percent of PCs. At the time, it lagged behind Windows ME, the 13-year-old Windows NT and various flavors of Linux.

"The big question is if and when are the masses going to switch?" Net Applications analyst Vince Vizzacarro said in a newsletter accompanying the statistics. "While Microsoft was late to market with Vista, Apple's taken advantage and is now up to a combined 6.38 percent market share. It looks like the market is buying Vista on new PC purchases, but there isn't a significant percentage of people upgrading existing PCs. I expect this trend to continue through the rest of 2007."