Will Windows 7 boost Apple sales?

Over the past decade, Mac shipments have grown with nearly every new Microsoft release

As if Steve Ballmer didn't have enough to worry about after last week's Sidekick/Microsoft (MSFT) Danger debacle, here's a bar graph that may add to his miseries.

The graphic (shown full-size below the fold) comes out of a report to clients issued Monday by Broadpoint AmTech analyst Brian Marshall. Anticipating the release of Windows 7 next week (Oct. 22), Marshall reviewed Mac sales figures over the past 10 years to analyze the impact of the four previous Windows launches:

• Windows 98 (launched on June 25, 1998)
• Windows 2000 (launched on February 17, 2000)
• Windows XP (launched on October 25, 2001)
• Windows Vista (launched on January 30, 2007)

His findings:

"We have concluded that no negative correlation exists on Apple's (AAPL) hardware sales when Microsoft launches a new OS. Ironically, we believe new OS launches from MSFT may have even acted as a 'delayed accelerant' to AAPL's computing sales."

The chart suggests that Vista's well-publicized problems were the real accelerant, providing fodder for more than two years of Get A Mac ads.

[Click to enlarge]

Correlation is not causation, of course, and Marshall is quick to add that "AAPL's success (or failure) in the computing market is largely idiosyncratic (or company-specific) in nature and not dependent on others in the industry."

Still, he thinks that despite Windows 7 -- if not because of it -- Apple could double its global PC market share from about 4% today to 8% over the next five years.

[Follow Philip Elmer-DeWitt on Twitter @philiped]