You need to use the FireWire (or i-link dv socket, as it's only a 4 pin firewire port) found on the back under the cover near your USB socket and power socket, as shown here:
It's best to use FireWire with things like this if you can, lots of threads explaining why. Plus iChat will only use FireWire cameras and not USB cameras unless you buy a plugin for it.
I have a similar older JVC camera I use at work, actually just used it to record a school production at work (iMovie'd and iDVD'd ofcourse!) I hope your's has better image quality and light control than the one I use!