I've taken the liberty of adding Trent, Christian and Martin to the nosy
list as I know they are actively, if reluctantly interested in this.

This patch allows the distutils to cross-compile on Windows.  It has
been tested on x86 and amd64 platforms, with both platforms successfully
able to natively and cross-compile extension modules and create binary
distributions.

To cross-compile, specify '--plat-name' to the build command (valid
values are 'win32', 'win-amd64' and 'win-ia64').  This option name was
chosen to be consistent with the bdist_dumb command.  I've included the
docs I added below (which are also in the patch), but note that as with
native compilation using distutils, it's not necessary to set any
environment variables or do anything else special with your environment
to make this work.

The patch also adds a x64 target for the 'bdist_wininst' target, which
it creates as distutils/command/wininst-9.0-amd64.exe.  This executable
is necessary even for bdist_wininst to work natively on x64, but is
still included here for simplicity.
    
To assist with testing, I've also added a distutils setup.py script to
the PC/example_nt directory.  This is capable of creating bdist_wininst
executables for both native and cross platforms; 'setup.py build
--platname=win-amd64 bdist_wininst' will create an amd64 installer on an
x86 machine.

The patch has not been tested with a Visual Studio environment without
cross-compile tools installed - it will obviously fail, but its not
clear how ugly this failure will be.

Below is the text I added to docs/distutils/builtdist.rst:

  Cross-compiling on Windows
  =====================

  Starting with Python 2.6, distutils is capable of cross-compiling
between Windows platforms.  In practice, this means that with the
correct tools installed, you can use a 32bit version of Windows to
create 64bit extensions and vice-versa.

  To build for an alternate platform, specify the :option:`--plat-name`
option to the build command.  Valid values are currently 'win32',
'win-amd64' and 'win-ia64'.  For example, on a 32bit version of Windows,
you could execute::

     python setup.py build --plat-name=win-amd64

  to build a 64bit version of your extension.  The Windows Installers
also support this option, so the command::

     python setup.py build --plat-name=win-amd64 bdist_wininst

  would create a 64bit installation executable on your 32bit version of
Windows.

  Note that by default, Visual Studio 2008 does not install 64bit
compilers or tools.  You may need to reexecute the Visual Studio setup
process and select these tools.