OSX includes terminal emulation software that you can use from the command line, so we only need to install the USB drivers for the cable.
Fetch the installer package for the USB drivers from here: http://sourceforge.net/projects/osx-pl2303/
If using Lion, try this driver here http://changux.co/osx-installer-to-pl2303-serial-usb-on-osx-lio
Both downloads are standard Mac installers. Accept all defaults when prompted.