Windows Vista has more to fear from Windows XP than rival operating systems, according to an industry analyst.

A survey of 600 companies with more than 1,000 employees in the US and Europe by Forrester Research found that Microsoft's six year-old XP has become standard in enterprises.

Around 84 per cent of Microsoft PCs run Windows XP, up from 67 per cent a year ago.

Only a third of survey respondents intend to start Vista deployments by the end of 2008, and a further 17 per cent will start the process in 2009 or 2010.

"Vista's biggest competition is not Apple or Novell or Red Hat, it is Microsoft itself with XP," the report said.

Forrester Research also found a significant number of companies looking forward to Service Pack 3 for Windows XP, which is due early next year and is supposed to be the last major upgrade.

Microsoft has already extended its deadline to end support for Windows XP, offering an additional five years past the original 2009 cut off date.