connecting usb to virtual machine

I'm using Backtrack 5 in a virtual machine under windows 7. I've connected as USB WiFi reciever to my laptop and told the virtual machine to connect to it. When I enter "airmon-ng" it doesn't seem to recognize the USB device. I've installed the USB driver using Windows and thought the virtual machine would find it. Do I need to load some sort of tool? What am I doing wrong?

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