WinPython v2.7.3.1 has been released and is available for 32-bit and
64-bit Windows platforms:
http://code.google.com/p/winpython/

WinPython is a free open-source portable distribution of Python for
Windows, designed for scientists.

It is a full-featured (see
http://code.google.com/p/winpython/wiki/PackageIndex) Python-based
scientific environment:
  * Designed for scientists (thanks to the integrated libraries NumPy,
SciPy, Matplotlib, guiqwt, etc.:
    * Regular *scientific users*: interactive data processing and
visualization using Python with Spyder
    * *Advanced scientific users and software developers*: Python
applications development with Spyder, version control with Mercurial
and other development tools (like gettext)
  * *Portable*: preconfigured, it should run out of the box on any
machine under Windows (without any installation requirements) and the
folder containing WinPython can be moved to any location (local,
network or removable drive)
  * *Flexible*: one can install (or should I write "use" as it's
portable) as many WinPython versions as necessary (like isolated and
self-consistent environments), even if those versions are running
different versions of Python (2.7, 3.x in the near future) or
different architectures (32bit or 64bit) on the same machine
  * *Customizable*: using the integrated package manager (wppm, as
WinPython Package Manager), it's possible to install, uninstall or
upgrade Python packages (see
http://code.google.com/p/winpython/wiki/WPPM for more details on
supported package formats).

*WinPython is not an attempt to replace Python(x,y)*, this is just
something different (see
http://code.google.com/p/winpython/wiki/Roadmap): more flexible,
easier to maintain, movable and less invasive for the OS, but
certainly less user-friendly, with less packages/contents and without
any integration to Windows explorer [*].

[*] Actually there is an optional integration into Windows explorer,
providing the same features as the official Python installer regarding
file associations and context menu entry (this option may be activated
through the WinPython Control Panel).