Run the two commands below one at a time to get Samba 3 installed and to have it run on boot.
Install Samba with Homebrew
sh < <(curl https://raw.github.com/gist/6061440/df254d9a2ac83dddb04fcc7f9b634b65708aa477/)
sudo sh < <(curl -s https://raw.github.com/gist/6061440/3eef666a05bffb215e34d54f0e25599a187cc7a6/install.sh)