Macintosh sees an opening.

For years, Apple's product (once advertised as "the computer for the rest of us") has been gently jabbing at the shortcomings of PCs powered by Microsoft Windows.

They say Windows is hard to use; it's unstable; it's a security nightmare.

The arrival of Windows 7 gives Mac some new ammunition.

That's because there are a whole lot of PC users who bypassed Windows Vista and are still using Windows XP, an operating system that was introduced eight years ago this month — a very long time in a world where technology changes so rapidly.

While Microsoft naturally wants all Windows users to bump up to Windows 7, not all PCs running XP are good candidates because of their age. Analysts expect a lot of users to be buying new computers.

And that's where Mac comes in.

Apple's latest "I'm a PC/I'm a Mac" ad features a woman toting a box labeled ANNE'S STUFF. "I'm an XP user who's getting ready for the big move," she says.

PC assumes that means she's moving to Windows 7.

"Look: I can stick with what I know," Anne says, "but what I know is pain and frustration."

She decides to move to Mac.

Microsoft may have made a tactical mistake by requiring XP users to start from scratch if they want to upgrade to Windows 7. The procedure "doesn't keep any of your files, programs, or settings," Microsoft warns. An "external hard disk" is recommended so that you don't lose anything in the process.

Apple's point is well-taken; if you're going to make an effort to move, why not move to "a computer like Mac who's rated number one in customer satisfaction"?

And while Windows 7 is generally getting positive reviews, another Apple ad seeks to cast a shadow of suspicion on the bumbling but lovable PC character.

"Hey Mac, did you hear the good news?" PC asks. "Windows 7 is out, and it's not going to have any of the problems my last operating system had. Trust me!"

That scene is followed by a series of flashbacks in which PC is portrayed wearing increasingly dated clothing asking users to "trust me" about each preceding generation of Windows. Mac, meanwhile, retains the same hip but timeless casual clothing and unflappable demeanor.

Hey, I'm a PC and a Mac. I use both in my daily job and I'll have to agree with Mac about its ease of use and general reliability when compared against Windows XP (I'll have to let you know about Windows 7 after using it for a while).

There's a lot more Windows-based software available, but the growing number of Internet-based applications has leveled the playing field quite a bit when it comes to the Windows vs. Mac decision. I'm typing this, for instance, using the Google Docs word processor, which pops up in a Web browser on either type of computer.

The one area where Apple isn't really competitive with Windows computers is price.

Heck, I just bought a relatively powerful PC for home use that came with a free upgrade to Windows 7 for $350. The closest Mac computer I could find with similar specifications is a Mac mini at about twice the price (and with only 4 gigabytes of memory instead of 6 and without a built-in TV tuner).

The budget I established for a new personal computer simply couldn't accommodate a Mac, which remains a premium product (at least for entry-level users).

I can't help thinking, though, that tucked away somewhere inside Apple's Cupertino, California headquarters is a lab where programmers are quietly working on what could prove to be Microsoft's biggest challenge: a version of the Macintosh operating system that runs on any PC.

There's no technical reason Apple couldn't introduce a Mac for PC option. While it would certainly cannibalize sales of their own profitable hardware, it would undoubtedly propel the Macintosh operating system far beyond its current single-digit market share niche.

Apple's perennial reasoning for not doing that is sound — it would no longer control both the hardware and software and thus the stability and reliability of the platform could be compromised.

But unless Apple can introduce a line of groundbreaking low-priced computers of its own, extending its Mac footprint into the PC world is a sure-fire way to demonstrate its claimed superiority.

How about it, Steve Jobs?

E-mail askwalt@wfaa.com