Update 4 (2008-01-16): RC1 has been removed. See http://pypi.python.org/pypi/Shapely/1.0rc2.
Update 3 (2008-01-14): I have confirmation from a Vista user and uploaded the installer to the Python Package Index: Shapely 1.0rc1.
Update 2 (2008-01-14): Grab an installer with new and improved DLLs from the same URL below.
Update (2008-01-14): apparently the GEOS DLLs don't load on Vista. I'll have a fix ASAP.
Thanks to distutils, even a know-nothing Linux zealot like myself can make Python distributions for Windows. Shapely-1.0rc1.win32.exe [MD5, SHA1] includes GEOS 3.0.0 and with just a few clicks you get a fully documented Python geometry package. You'll need to install ctypes if you are using Python 2.4. Some users may need to install msvcp80.dll.
Shapely is distributed under the familiar 3-clause modified BSD license, which means that you're pretty much free to do what you will with it.