This is my first instructable so I wouldn't mind if people posted their opinion.
NOTE: Pictures will be added at a later date when I make the second fan, the first one (which I am writting this instructable from) was simply a test to see if it would infact work.
Step 1: Preparing the USB Cable
Once the protective jacket has been removed, remove some of the shielding such that the 4 wires which make up the USB cable are exposed.
Cut the white and green wires short (to the protective jacket) as they will not be needed for powering the device.
Step 2: Preparing the power wires.
Step 3: Taking apart the fan.
Step 4: Connecting the USB wires to the fan's battery terminals.
Step 5: Making the conections permenant.
NOTE: After completing this instructable, I've discovered that the USB port is too powerful fo the fan I chose so a resistor wired in series before the connection to the fan would help lower the power and therefore not overload the fan/motor. This is as simple as soldering a resistor of high enough resistance to decrease the voltage to around 3 volts (from thew 5 that USB puts out).