, Microsoft's senior director of Windows client product management, said any customers still running "should definitely move to Vista." And with , she urged users of that operating system to consider "how much money am I spending keeping XP alive vs. moving on?"

Schuster, who also wrote a post about upgrade issues on the "Windows for your Business" blog that Microsoft launched last week, said users who skip Vista risk having their software vendors end support for the applications they're running on XP.

In addition, Schuster noted, most companies may take up to two years after 's release to deploy it because of all the required application testing and employee training. As a result, Vista holdouts could go five years or more between upgrades, she said.

Forrester Research Inc. surveyed 962 IT decision-makers about their Vista plans last summer. In a report issued in late January, Forrester said 30% of the respondents were already deploying Vista, while another 27% planned to roll it out this year or in 2010.

But the survey was conducted before the worsening of the economic downturn. Paul DeGroot, an analyst at Directions on Microsoft in Kirkland, Wash., said that in the current climate, Microsoft's reasons for upgrading may not be enough to get users to move to Vista.