Dell has finally made it official and plans to pre-install Ubuntu Linux on some desktops and notebooks. Red Hat was left out of the party–but the company still has some reason to celebrate. What can you expect from Dell’s Linux desktops? Here’s a sampling of thoughts from The VAR Guy.

First, Linux is not about to topple Windows Vista or Windows XP. For all the Linux fans who think Microsoft is dead meat, please read The VAR Guy’s unique analysis of the software giant’s latest financial results. You won’t believe how tiny Red Hat remains compared to the Mighty Microsoft.

Still, Dell’s decision to pre-install Ubuntu Linux on selected desktops and notebooks represents a critical tipping point for desktop Linux. And it’s an admission of sorts that Windows Vista won’t be for everyone–even when Microsoft cleans up all the bugs. Dell’s move signals that customers–rather than Microsoft–now control their own desktop destinies. Even Red Hat, which was left out of the Dell desktop deal, is telling customers that this is a significant day for Linux.

Within a year or two, The VAR Guy thinks that Mac OS and Linux together could control more than 10 percent of U.S. desktop and mobile PC sales. It has been at least a decade–maybe more–since Microsoft commanded less than 90 percent of the U.S. desktop market.

But let’s not get ahead of ourselves. Ubuntu Linux isn’t for everyone. Dell needs to carefully position the Ubuntu systems. The company will need to clearly communicate–over and over again–which applications, printers and peripherals work with Ubuntu. In fact, The VAR Guy suspects Dell will up-sell customers with Ubuntu-compatible peripherals that are guaranteed to work with Linux right out of the box.

This is a big day for Linux. But it could also become a black eye for the open source movement if Dell fails to manage customer expectations appropriately. All it takes is a few hundred disappointed customers to whip up a storm of complaints on the Internet.