1) Go to http://emacsformacosx.com/ and download Emacs 23.3; install it.
2) For commandline use in Terminal, create the following script in your ~/bin or somewhere at the top of your $PATH:
$ more bin/emacs
EMACS_APP=/Applications/Emacs.app # <- UPDATE THIS IF NEEDED
exec $EMACS "$@"
3) Run it as normal.