It’s quite easy. Make sure python is installed, then
1) Download setuptools here(python2.7, 32bit),
2) Install that, it will try to find the python environment from registry,
3) Go into your python directory in case you have multiple version of python, and run Scripts\easy_install.exe wxpython.
More information can be found at http://pypi.python.org/pypi/setuptools#windows