You should be able to open Two instances (windows) of Finder on your desktop (after clicking on the Finder icon in the Dock for one instance, then click on "FIle" in the top Menu Bar and select "New Finder Window" to call up a second FInder window), select the source internal Superdrive in the left hand column of one Finder Window, and drag the wanted files from that Superdrive to the external Superdrive shown in the other Finder window's left hand column. Select burn then for the external Superdrive. That should do it.
(Any of you fellow Users have a simply way then my suggested method? Feel free to jump in here.)
Hope this helps