Tunnelblick is free opensource GUI for MAC OS X its a great alternative to OpenVPN GUI.
This thread will show you how it is easy to configure and use Tunnelblick, if you used a OpenVPN GUI before you can copy your configuration and your certificate files to your MAC.
You can get Tunnelblick from here.
Its possible to import your already existing configuration;)
In my case I used my configuration from OpenVPN GUI, only one thing must be done the paths in your config.ovpn should be fixed to your new location of the certificate files. Here is a example: