The milestone was revealed last week when the company released its quarterly earnings report.
The second quarter also set a record for Microsoft of US$16.37bn in revenues, a 30 per cent increase over the same period last year.
"We are pleased with the progress of Windows Vista in the market," said Kevin Johnson, president of Microsoft's platforms and services division.
"We have hit our stride with partners and customers and look forward to the release of our first service pack later this quarter."
Microsoft claimed that its Client branch has grown by 20 per cent since Vista was released to business customers in November 2006.
Chairman Bill Gates predicted the 100 million Vista milestone at the operating system's consumer release in January 2007.
Vista sales had topped the 60 million mark by July, but excitement faded when PC manufacturers found that demand for Windows XP remained strong and began to offer the old OS as an option on new PCs.
Windows Vista sales top 100 million
By Shaun Nichols on Jan 29, 2008 3:45PM