After spending many hours trying to get FreeTDS and unixodbc to run on a Mac OS X 10.8 system with the python module, pyodbc, I eventually came to this recipe, which is remarkably simple thanks to homebrew. I also found unixodbc was unnecessary and I couldn't get it to play well with FreeTDS, so this install does not include unixodbc. See also http://www.acloudtree.com/how-to-install-freetds-and-unixodbc-on-osx-using-homebrew-for-use-with-ruby-php-and-perl/ and http://www.cerebralmastication.com/2013/01/installing-debugging-odbc-on-mac-os-x/.
Prerequisites: Be sure you have XCode and the Commandline Tools for XCode installed from Apple. Also install homebrew followed with brew update and brew doctor.
Install FreeTDS:
brew install freetds
Test your install: