Windows Vista may yet prove to be an unstoppable juggernaut, but statistics released by a market research firm show the new operating system (OS) is barely denting existing market leaders.

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

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

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

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% of PCs. At the time, it lagged behind Windows ME, the 13-year-old Windows NT and various flavours of Linux.

"The big question is if and when are the masses going to switch?" Net Applications analyst Vince Vizzacarro said. "While Microsoft was late to market with Vista, Apple's taken advantage and is now up to a combined 6.38% 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."

Some analysts have predicted that despite Microsoft's intention to spend half a billion dollars marketing Vista, conversions from XP won't be the norm until 2009.

Statistics for the first week of February – Vista officially launched 30 January – were mixed. Current Analysis found sales of PCs – with Vista preinstalled -- were up 173% from the week before. PC sales were also up 67% from the same period in 2006. But Current Analysis itself pointed out that the sales leaps were exaggerated partly by slowing sales as retailers and OEMs wound down their XP-based inventory.

By comparison, NPD Group found that first-week sales of boxed copies of Vista were down 60% compared with first-week boxed copies of Windows XP five years earlier.

Neither group has released statistics of Vista sales in subsequent weeks, though NPD analyst Chris Swenson is expected to release first-month retail sales of the new OS soon.