Just in case you ever have to do it again, here's a way to do it using macports...
sudo port install mysql5 +server
sudo port install mysql5-server
sudo env ARCHFLAGS="-arch x86_64" gem install mysql --no-rdoc --no-ri -- --with-mysql-config=/opt/local/bin/mysql-config5
# setup mysql.sock
sudo ln -s /opt/local/var/run/mysql5/mysqld.sock /tmp/mysql.sock