The dollar value of retail box copies of Vista sold during the week of Jan. 28 also fell 32 percent from the value of XP box copies sold during its first week in October 2001, according to figures from Port Washington, N.Y-based NPD Group Inc. released Thursday.

However, retail sales of PCs, virtually all of them sporting the new Vista OS, were up 67 percent over the same week in 2006. While that is hardly an apples-to-apples comparison -- many stores were clearing out their XP inventory in the weeks leading up to Vista's launch -- "it still reflects a fair bit of growth," according to Chris Swenson, a software analyst with NPD. He declined to release exact dollar figures.

Swenson's interpretation of the seemingly-in-conflict numbers? Consumers are "getting the message that they need a more robust system to take advantage of some of the new features in Vista," he said in a statement. Thus, a smaller number of consumers are opting to upgrade their existing hardware with Vista out of fear that it won't be powerful enough.

Vista's poor retail sales contrast with Office 2007's first-week retail sales, which more than doubled Office 2003's first-week sales.

The good news for Microsoft: Consumers who are upgrading to Vista on their older machines are opting for pricier, higher-end versions of it. The average selling price of Vista was US$207.13, up 66 percent from the average selling price of XP. That was due in part to the fact that more than 30 percent of the copies of Vista sold were the Ultimate version, which for $399.