Recently I had the opportunity to meet with Jim Allchin, Microsoft"s group vice president in charge of platforms, to talk about the future of Windows. As it turned out, however, what he has to say about Linux is equally interesting.

Microsoft gave up pretending that Linux isn"t a threat to its Windows server business a long time ago. But when the soft-spoken Allchin first brought up the server market during our conversation that afternoon, he dropped the L-word with such candor that I was frankly shocked.

"Linux is the expected winner," Allchin says, "with its lineage from Unix. But we"re happy, because we"re winning market share."

Got that? Not only is Linux a formidable competitor in the server market, but now Microsoft actually paints itself as the underdog.

It makes sense, if you buy into the company"s long-held position that Linux"s growth comes at the expense of proprietary Unix OSes such as AIX, HP-UX, and Solaris, rather than from the Windows customer base. No matter what gains Microsoft might make in the server area, if you replace all that Unix iron with Linux boxes, the free OS"s server-side market share will be truly massive.

But the majority of our conversation that afternoon focused on the client side. Here Allchin was far less charitable, attributing Linux"s reported growth in the desktop market to something he called the "24-hour Linux phenomenon."

According to Allchin, most customers who buy a new computer outfitted with Linux instead of Windows are doing it solely as a cost-cutting measure. They avoid the Windows license fee at the cash register when they ask for systems with Linux preinstalled. Once they get the hardware home, however, that Linux OS is quickly erased and replaced with a pirated copy of Windows -- often within 24 hours.

Allchin calls the practice of replacing the default OS with Windows "flipping," and he says it"s particularly prevalent in Asian markets, where software piracy is rampant. In China, he says, shipments of desktop Linux are actually declining. The reason? Vendors who once shipped systems with Linux preinstalled are now switching to free or low-cost versions of DOS. That"s because it"s a lot easier for a customer to flip a system loaded with that bare-bones OS than it is to flip a comparatively more Byzantine Linux system.

I was tempted to suggest that maybe there was an opportunity for Microsoft to start marketing MS-DOS again, but I didn"t.

Indeed, Allchin has a point. Although anecdotes such as the ones he cited are obviously self-serving, it"s wrong to overstate Linux"s actual growth in the desktop market. Whether a customer sends revenue Microsoft"s way or not, a machine that ships with Linux but ends up running Windows is not a gain for Linux.

Keep that in mind if you"re championing desktop Linux for your company. Take it slow. Right now, Linux is best-suited to workers who use a limited, tightly integrated set of Web-based and productivity applications. Day by day that"s starting to change, but for the time being you won"t help your cause by repeating statistics that don"t accurately reflect market realities.

Thankfully, in the datacenter the decision is much less difficult. You heard it from Microsoft"s platform guru himself: Server-side Linux has arrived and is going strong. Sounds like a no-brainer -- unless you like rooting for the little guy. Then buy Microsoft. (Did I get that right, Jim?)