This is no problem for ARM processors since they are bi-endian (as PowerPC).

Source: http://en.wikipedia.org/wiki/Endianness#Bi-endian_hardware

There is nothing in Windows which requires fixed endianness. While all known versions of the OS have been shipped on little-endian machines (except XBox 360, albeit running highly modified version of NT Kernel), there is very little dependency on the endianness for all modules except format parsers and network API. Changing that is a relatively simple undertaking, much simpler than building a new version of kernel, for XBox, for example

That can't be correct, since I remember running Windows NT 4 on a PowerPC system.

PowerPC (except PPC970 aka G5, as I recall) is bi-endian (configurable endianness); so are Alpha and Itanium which also had Windows NT ports.

Alpha is most definitely not a bi-endian architecture; it's little-endian only. PowerPC chips can be either, but the vast, vast majority are big endian.

Incorrect. The Cray T3E used Alpha processors in big-endian mode.