Today Apple announced it sold more than 2 million copies of Mac OS X 10.5 Leopard in its first weekend. “Early indications are that Leopard will be a huge hit with customers,” said CEO Steve Jobs in the press release, though he might be just a teensy bit biased.

I’m guessing Apple is seizing this opportunity to gloat because demand for Leopard – like the iPhone -- will never be so high as on its first weekend.

But whether 2 million is a big number depends on how you look at it. For example, Leopard’s achievement compares very well to its predecessor, Mac OS X 10.4 Tiger, which took 5 weeks to sell 2 million copies.

Comparing Leopard to Vista, the latest incarnation of Microsoft’s Windows, shows the value of holding more than 90 percent of the operating system market. Though widely criticized, Vista sold 20 million copies in its first two months – nearly the same number as every Leopard-capable Mac in existence. (Apple Chief Operating Officer Timothy Cook estimated during the company’s recent earnings conference call that currently about 21 million Macs are Leopard capable – an impressive number considering the large number of older Macs that do not meet Leopard’s minimum specs.) Windows XP sold 17 million copies in its first two months back in 2001.

During Microsoft’s recent earnings conference call, the company reported that 85 million licenses for Vista had been sold this year. True, most of those were pre-installed on Windows PCs sold by the likes of Dell and Hewlett-Packard, but still. It’s a daunting number from the Mac perspective (not to mention the even smaller number of fans of the Linux OS).

Then again, Leopard already has been hacked to run on ordinary Windows PCs. Apple surely won’t be happy about it, but what if it catches on? We might well hear Apple report at their January earnings conference call that hundreds of thousands of copies of Leopard were “purchased with the intent of being run on non-Apple hardware.” How crazy would that be?