The surprise decision to launch Vista, billed by analysts as Microsoft’s most important product for a decade, from London is a publicity coup for the British capital. When he launched Windows XP, Vista’s predecessor, in 2001, the Microsoft chairman kicked off the day by ringing the opening bell on the Nasdaq stock exchange in New York. Mr Gates then shared a stage with Rudolph Giuliani, the Mayor of New York at the time, as Microsoft threw parties around the world, including a circus performance in Times Square.

For Vista, however, the world’s richest man will make the briefest of stopovers. It is understood that he plans to spend one hour in London, after which he will depart for Edinburgh, where he will join the Microsoft Government Leaders’ Forum.

That the Edinburgh event, which has been planned for months, clashes with the Vista launch date indicates how tight the deadline for the release of the software has become. The system, which cost an estimated $7.5 billion to develop over half a decade, has been delayed by two years.

Vista and Office 2007, the applications suite that will be launched at the same time, are crucial for Microsoft. The two products are expected to account for the lion’s share of Microsoft’s earnings, with Vista’s predecessors contributing $10 billion of the company’s $16.5 billion pre-tax profit last year.

However, worries persist that Vista, even at this late stage, is not quite ready for widespread adoption.

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