You can follow that Instructable or just watch the video version:
Step 1: Dismantle the drive
NOTE: every drive is different "inside", so it's a bit useless show you where is located. But you can see the picture to know what you are looking for.
Step 2: Making of the blades
Mark 8 identical cloves on the "cd", then cut them with a cutter.
Step 3: Mount the blades
Make a small hole in the bottom. Cut off 1/3 in height and hack enough space for the blades.
Insert the blades (4 or 8) and secure them with super-glue. Let it dry :)
Step 4: Prepare the usb cable
Step 5: Insert the wires into the sheath
tie the wires (3 irons +2 from the usb) to a longer iron wire threaded in the sheath.
Pull the longer iron wire from the other side of the sheath, in order to make slip inside all the wires.
Step 8: Test it..!
you can watch a video clip showing this cool Usb Fan here:
NOTE: thank to the iron wires, you can model the cable to any shape ;)