Microsoft Corp. posted a 65 percent rise in quarterly profit Thursday, topping Wall Street estimates thanks to better than expected demand for its new Windows Vista operating system.

Shares of Microsoft rose 5 percent after the announcement, in which the world's biggest software company also forecast 2008 profit at the midpoint of a range of analyst estimates.

"The strength of Vista is really driving this," said Kim Caughey, analyst at Fort Pitt Capital Group. She added that the company had set "manageable expectations for the full year 2008, which generally allows them some headroom."

Microsoft posted a net profit of $4.93 billion, or 50 cents per diluted share, in its fiscal third quarter ended March 31 versus a profit of $2.98 billion, or 29 cents per share, in the year-ago period.

Excluding tax benefits and a legal charge, Microsoft earned 49 cents per share, beating the average analyst forecast of 46 cents, according to Reuters Estimates.

Revenue rose 32 percent to $14.4 billion. Analysts, on average, had forecast revenue of $13.89 billion, with estimates ranging from $13.73 billion to $14.09 billion, according to Reuters Estimates.