Microsoft Chairman Bill Gates estimated on Tuesday that Windows Vista has an 80 percent of chance of shipping to consumers by its twice-delayed January launch date, leaving many scratching their heads about the 20 percent odds of another delay.

Speaking to Redmond’s business partners in South Africa, Mr. Gates left open the possibility of a further postponement if beta testers discover more problems with Vista. The software is scheduled to ship to large companies in November, and smaller companies and consumers in January.

“We’ve got to get this absolutely right,” he said during a presentation in Cape Town, according to Dow Jones Newswires. “If the feedback from the beta tests shows it is not ready for prime time, I’d be glad to delay it.”

Microsoft shares fell $0.37 to $23.13 in recent trading. Other tech issues also trended lower amid news of deadly bombings on trains in Mumbai, India, that killed an estimated 135 people and injured hundreds of others.

The world’s largest software company is spending between $8 billion and $9 billion to develop Vista and its upgrades for its Office product, which has also been repeatedly delayed.

Vista had originally been scheduled to ship in 2005, was pushed back to 2006, and then January 2007 (see Microsoft Delays Vista, Again).

The delay on Office in March followed closely on the heels of a delay in Vista. The company said that Office would be available to large businesses in October and in January for consumers and small businesses (see Office Delayed, Along with Vista).

But in June, Microsoft again pushed back the ship date for Office to the end of the year for large business customers and early 2007 for consumers and small businesses (see Microsoft Delays Office Again).

The most recent postponement for Office was attributed to “product performance” issues discovered during beta testing. At the time, Microsoft said it might need to reevaluate the timing of the Vista release as well, because it wants the two to coincide.

1,000 Allies

Despite the repeated delays of Vista, Microsoft is claiming broad partner support for when it’s ready. At its worldwide partner conference in Boston on Tuesday, the company said that nearly 1,000 global independent software vendors would deliver a range of applications for the operating system.

Sanford Bernstein analyst Charles DiBona remains confident in Microsoft’s ability to deliver. “We currently believe that [Microsoft] remains on track to meet its previously announced launch dates for Vista and Office 2007,” he wrote in a research note.

In South Africa, Mr. Gates said he hoped Office would be ready by December. He is also visiting South Africa to attend a forum Microsoft is sponsoring that has invited African government leaders and Bill Clinton to discuss how technology can enhance competitiveness on the continent, and to examine AIDS and other health projects with his wife for the Bill and Melinda Gates Foundation.

Mr. Gates also introduced a plan to offer cheap Internet access in the country in partnership with the South African mobile phone operator MTN. Customers will be able to buy a PC and have access to Internet connectivity for a monthly fee.

Contact the writer: MCohn@RedHerring.com