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Gates opened a technical support centre destined to serve European customers, saying the group planned to expand operations in Romania, which joined the European Union along with Bulgaria on January 1.

"It's very important for Microsoft that the support work being done here will help our customers throughout Europe handle their most complex problems," Gates said as he opened the centre.

"This is something that we expect to continue to invest in and I think it will play a bigger and bigger role."

Vista was launched by Microsoft at a glitzy party in New York on Monday night before being rolled out to retailers in 70 countries worldwide. Gates has since stopped in London and Edinburgh and is also expected in Paris.

The Vista software, which has new graphics, improved functionality and more rigourous security, took five years and six billion dollars (4.6 billion euros) to produce.

Gates said Thursday that Microsoft would increase the frequency of new releases.

"We'll have major releases of Windows every three years," he said.

Responding to comments from Romanian President Traian Basescu, who said that Romania had been one of the worst countries for piracy of Microsoft products in the 1990s, Gates replied: "Piracy is an important issue. But as an economy develops, there is more understanding of rules and the rate of piracy drops."

He added: "Things are changing on a gradual basis but they are moving in the right direction."

Basescu helped open the support centre along with Gates and Prime Minister Calin Tariceanu.