I made a custom installer/uninstaller for the AVRISP mkII open source usb driver. Pretty handy if you need it. I use them for distributing the AVRISP mkII's to a few remote places needing firmware updates on some avr boards. Note that this is the open source libusb driver that comes with winavr. As far as I can tell, the driver only works for avrdude/winavr (programmers notepad, etc), not AVR Studio.
1. Make sure any existing drivers are uninstalled.
2. Plug in the AVRISP mkII to a usb port
3. Use the driver installer
Not sure about meeting open source licensing requirements here, but this is a pretty obscure.