Yes, it is in the port tree. You will have to get your sources and ports (Chapter 5 of the Quick Guide on your desktop) and once you have those you will need to open konsole (KMenu -> System -> konsole), su to root and then
cd /usr/ports/security/vpnc && make install clean && rehash
and that will download anything you should need and compile that application. read what it says near the end of the install.
I would set konsole's history unlimited (Settings -> History -> Set Unlimited) so you can find any errors that might occur. It probably also installs man pages so you should be able to
after the install and read what they tell you.