The Windows product development team has posted some information about Windows 8 and execution on the Arm® processor.  Here’s the first paragraph from that post:

One of the notable aspects of Microsoft Windows has been the flexibility the architecture has shown through shifts in technology and expansion of customer usage over time. What started out as an operating system for one person working solo with productivity software is now the foundation of a wide array of hardware and software technologies, a spectrum of connected Windows products, and an incredibly flexible approach to computing. With Windows 8, we have reimagined Windows from the chipset to the experience—and bringing this reimagined Windows to the ARM® processor architecture is a significant part of this innovation. Expanding the view of the PC to cover a much wider range of form factors and designs than some think of today is an important part of these efforts. Windows on ARM enables creativity in PC design that, in combination with newly architected features of the Windows OS, will bring to customers new, no-compromise PCs.

See the full post at http://blogs.msdn.com/b/b8/archive/2012/02/09/building-windows-for-the-arm-processor-architecture.aspx.