i have an ephoto 1680. aside from a usb-serial adapter, i don't know of any usb cords specifically for the 1680.
i use a smartmedia card reader. these are inexpensive devices (less than $100) that plug into the usb port. i prefer them. they are faster than serial port transfer and you conserve your camera's battery power.
another alternative, if you have a powerbook, is to use a smartmedia-pcmcia card adpater. these are also less than $100 and let you plug the memorycards directly into the computer.