The Peperoni Output plugin supports USB-DMX output devices produced by Peperoni Light.
On all Linux distributions, you need to install libusb. If you install QLC+ with the Ubuntu Software Center or some other automatic installer tool, this library will be installed automatically for you.
Nothing special is needed for Mac OS X. All required components are already inside the Q Light Controller Plus application bundle because QLC+ uses the OS X native USB interface.
You must install the Peperoni USBDMX Windows drivers.
Usually these come on a CD along with the Peperoni device you've bought.
If after installing the driver, QLC+ still doesn't detect your Peperoni device, copy the usbdmx.dll file you find inside the driver ZIP package (i386 folder) into the main QLC+ folder.