According to the spec on the Cannon site, this model does not have a headphone socket. As Chris says, the socket you are looking at is for both sound and video and takes a plug with an extra ring (i.e. ring1, ring2 tip and sleeve, rather than the ring, tip and sleeve of a headphone jack).
In order to transfer video to your PC you will need a firewire port on the PC and a firewire cable. You can buy a firewire card with free cable from Amazon for 7.99 which doesn't seem that expensive to me.
The camera also has a USB port, but I'm pretty certain that that is only for transferring still photos.
http://www.amazon.co.uk/Nisis-port-PCI-Firewir e-Card/dp/B00006JIMG