However, Gates said at a presentation in Cape Town to Microsoft software partners that he would delay the launch if beta testing uncovered shortcomings.
The Vista software has been subject to a number of delays. Beta users of software test products before their full commercial release in an effort to uncover problems.
"We got to get this absolutely right," Gates said. "If the feedback from the beta tests shows it is not ready for prime time, I'd be glad to delay it."
He said Microsoft was investing $8 billion to $9 billion in developing Vista and the company's next version of Microsoft Office, its key cash-generator. He said the company's software partners, in developing and adapting their own products for the two launches, would invest 20 times as much as Microsoft.
Gates said he hoped the next version of Office would be ready in December.
The new Vista operating system will have speech and visual recognition tools and be backed by strong security measures, he said. It would move away from reliance on easy-to-crack passwords to greater reliance on visual identification and software shields on Internet attacks.
He said the new Office would include the biggest set of innovations in more than a decade, citing its ability to work on documents simultaneously over the Internet.
The biggest market for these products soon will be China, Gates said. He said China was already the world's No. 1 mobile phone market and he expected it to be the world's top PC, broadband and software market within a few years.
"Everybody needs to be in China," he said. "Even if only 20 percent of the population is IT-active," he said, this is a huge number given the country's 1.3 billion population.
China's piracy of Microsoft software will decline, he predicted, as China becomes a bigger producer of intellectual property and sees "it will benefit as much as us" by implementing strong intellectual-property protection.
He expects the Chinese government — which accounts for what he said was 35 percent of the country's software sales — to buy all its software legally this year.
Gates is in South Africa to attend a Microsoft-sponsored forum of government leaders which gathers several African heads of state and former President Clinton in debates on how technology can improve the continent's competitiveness.
Gates and his wife, Melinda, also are visiting projects supported by their philanthropic organization, which has invested billions of dollars to fight diseases such as HIV- AIDS and malaria.
Shares of Microsoft dipped 8 cents to $23.42 in pre-market trading.