Download and install Git from MSysGit or Git SCM.
Download and install getopt.exe from the util-linux package into C:\Program Files\Git\bin. (Only getopt.exe, the others util-linux files are not used). Also install libintl3.dll and libiconv2.dll from the Dependencies packages (libintl and libiconv), into the same directory.
Suppose that Git is installed in the folder
c:\bin\gitand GnuWin32 in the folderc:\bin\GnuWin32.
Clone the git-flow sources from GitHub:
$ git clone --recursive git://github.com/nvie/gitflow.git