Steve,
I have put a pdf for a simple fm receiver implemented in vhdl as found on www://www.opencores.org in the code libarary in the schematics section as its got suitable diagrams which show how you can do it digitaly,although i think that most chip manufacturers dont implement the NCO as a digital system simply because its easier and gives better noise/jitter performance if its implemented as an analogue device where its implemented as a VCO.