Give the connection a title, keep the "Connect to" option blank, set the reconnect option to "Plain connection (no retry if failed)", set the emulation to VT100, and set the Device to "Serial/Modem". Go to Host Directory in Zoc and click on New. In my case, I am connecting to a Cisco Video Communications Server (VCS) so, some of the configuration parameters I show in the following screenshots are specific to the VCS. If you use Zoc, then here is the procedure for using the IOGear (or I suppose any device that uses the PL-2303 driver). It is a great app, but that is a blog entry for another day. I use Zoc Pro as a terminal application on my MBP and iMac. I didn't bother modifying the configuration, just click on Apply. In my case I saw a modem driver named "PL2303-". In Network Preferences, you should see the new network connection. Neither of these methods worked for me, just an FYI.
NOTE: The Prolific install guide (I found it online) said that you should be able to see the USB serial interface using System Profile or from the terminal using: ls /dev/tty.usbserial*. If you see this, click on "Network Preferences". When I connected the dongle, I received a prompt from OS X, which stated that a new Network Interface was detected.
I did a few more searches, focusing on software download sites and I found a link that worked:
Now, at this point I have spent an hour or two digging around and I am thinking I have old stuff that may need to be recycled. Obviously, those threads are dated because that link didn't work either.
To avoid boring readers to tears, here is a summary of what did not work: There were several problems finding the right driver. With a little Google magic, I was in business. Thankfully, the manufacturer affixed a label with a part number on the dongle. In fact, I didn't know what type of device it was at first. So, I wasn't holding out much hope on it working. I originally got it for an IBM thinkpad I had back in 2003 or 2004. Fortunately, I had an IOGear GUC232A USB to serial host adapter in my kit.