Look at your /var/log/messages after you connect your cable. It should be there.
For example, when I connect mine, it outputs:
Code:
[29149.216000] usb 1-1: new full speed USB device using ohci_hcd and address 5
[29149.428000] usb 1-1: configuration #1 chosen from 1 choice
[29149.432000] pl2303 1-1:1.0: pl2303 converter detected
[29149.432000] usb 1-1: pl2303 converter now attached to ttyUSB0
In my case, it's /dev/ttyUSB0