JVC is not known for having good tech support as they do not post drivers for this model.
The JVC-Canada site has a few drivers posted but nothing for the gr-d230u.
You will probably need to contact them.
Also, please realize that you cannot transfer video footage to the computer via the USB cable. You have to do that with a firewire port and cable. The USB port is only good for transferring still photos to the computer.