Throughout the computer industry companies of all sizes, from garage startups to Microsoft, are bracing for the possibility that their future will be in the hands of people like Sean Whetstone. The head of computer operations for Reed Specialist Recruitment, an employment service with operations on three continents, Whetstone recently upgraded his company's 6,000 desktop computers. Chief information officers order new Dells or HPs all the time. But the computers Whetstone brought in for his employees aren't the traditional metal boxes that sit next to desks or under monitors. They are "virtual" computers. Each employee has a keyboard and a...