In many ways, Apple is already a giant. Its US$118 billion market cap, which briefly surpassed Google's this year, is larger than that of Hewlett-Packard Co. Its sales, which are nearly $31 billion a year, have grown almost 40 percent annually the past five years. And, then there's its mindshare with the general public.

Still, Macs remain a small, albeit fast-growing, portion of the overall PC market. In the US, Windows PCs account for 11 out of 12 new computers sold in the most recent quarter, according to Gartner and IDC.

That fact that Microsoft remains the elephant and Apple the mouse accounts for why in the second, Jerry Seinfeld-free phase of the Windows ad campaign that kicks off Thursday night, Microsoft will continue to tiptoe around its smaller tormentor.

"It's Marketing 101. It clearly makes sense for the No. 2 guy to pick a fight with the No. 1 guy," said Eric Hollreiser, director of corporate communications for Microsoft. But with its ad counterattack, Microsoft does not need to spend too much time on Apple, he said. "There were some pervasive misperceptions that we needed to address. It's unmistakeable that we will focus on them. But we will quickly pivot to the positive values of Windows."

Why not return the favor and go after Apple for its recent problems launching MobileMe and iPhone 2.0, or the way it closely guards its technology?

Hollresier says Microsoft would rather get that message across subtly, through things such as its slogan, "Windows. Not Walls," which "provides differentiation."

"We wanted to talk about us, [and] have people hear what we have to say about Windows, not what we say about competitors," Hollreiser said.

The closest Microsoft will come to mentioning the 'A' word is at the beginning of the new ad, when a Microsoft employee, "Sean," who resembles the PC guy played by actor John Hodgman in Apple's ads, will say, "I'm a PC, and I've been made into a stereotype."

The 60-second commercial will air Thursday night at 9:30 p.m. Eastern Time, during NBC's The Office. A Web video version will be made available on YouTube and on Microsoft's marketing Web site at that time.

A preview version seen by Computerworld showed celebrities including author Deepak Chopra, actress Eva Longoria (and husband basketball player Tony Parker), and other accomplished but less famous notables talking about why they "are a PC."

The ad shows a wide range of people: a graffiti artist, an Obama blogger, a McCain broadcaster, a scuba diver in a shark cage, an astronaut, and a grizzled commercial fisherman.