This is how I replaced the USB cable on my Wacom Graphire 4 tablet. The tablet is now over 6 years old and still works great!
First, take off the back panel by unscrewing the screws and popping out the plastic tabs with a screwdriver. Once it is off, you can see where the USB cable is attached to the circuit board.
Take a look at this image: http://alturl.com/74a59
Each USB 2 cable contains black, white, green and red cables inside, along with a ton of tiny metal wires that surround them on the outside. You can actually see the outside wires on some of the USB cables that are made out of clear plastic, such as this one: http://www.outletpc.com/gh5115.html?gclid=COS9-5XYj7ECFbEBQAodSH_0DQ
Once you took off the back panel, you should see the 4 colored cords attached to the circuit board, along with a 5th cord. Write down the order of colors (for example, it might be red, green, white, black). The 5th cord (on mine it was to the left of the 4 colored ones) is actually part of the outer wi