Vusb Arduino Shield
this is a project how to use vusb with an arduino-usb-breakout. your pc will find an usb-keyboard if you connect the "shield usb" to an usb-port.
As you see in the Fritzing Sketch, just attach everything the right way and flash the vusb-keyboard example on your arduino. if you now unconnect the arduino usb and connect the new usb-port to your pc the device should come up as an usb-keyboard.
you'll need to install the vusb-library in your arduino-IDE. please use the links for more information, example-code and library-download.