Microsoft recently announced that it be providing a virtualised copy of Windows XP as a free compatibility add-on to Windows 7 Professional, Ultimate, and Enterprise editions.

The idea is to entice potential upgrade fence-sitters into taking the Windows 7 plunge by addressing one of the more widely cited concerns about the product: it will break legacy, Windows XP-era applications. And based on the amount of buzz surrounding this unexpected new feature, it would seem that Microsoft has hit a home run with its Windows XP Mode announcement.

Yet I fear that much of this excitement will turn to disappointment as IT shops begin to understand just what XP Mode really is and how limiting its Virtual PC-based underpinnings can be.

Simply put, XP mode is a bit of a half-measure of a solution cobbled together from various disjointed Microsoft technologies. Compared to something such as Mac OS X, which famously introduced one of the more elegant legacy compatibility solutions in the form of its integrated Mac OS 9-era application support, Windows 7's XP Mode is downright homely.

Before I dive into my reasons for disliking Windows XP Mode, it might be helpful to first review exactly what it is and how it works. Simply put, XP Mode is a virtual machine image file that contains a fully licensed and activated copy of Windows XP with Service Pack 3 installed.

The image is shipped in Microsoft's Virtual Hard Disk (VHD) format and is compatible with Windows Virtual PC 7, the company's new host-based desktop virtualisation tool.