On Windows, it looks like Python has to be started using absolute file path so it works fine.
You can change the file path of the plugin going to the 'Plugins -> Cli Tools -> Python -> Configure' menu action.
In that dialog, click the button at the right of the command line edit and browse until you find pythonw.exe binary.
Save, and close the dialog then restart Monkey Studio.
Python interpreter should works fine.
If you need to extend the PATH environment variable to make some python available, let see http://monkeystudio.org/node/177.