Hi pixelplucker, there is nothing built in to MoI for converting from sub-d cage to NURBS but you might try the plug-in that Pilou has the links to above, that may work for you if you have all regular topology (meaning every vertex has only 4 edges coming out from it).

Otherwise, if that does not do the trick for you the main tools for doing that type of conversion are the T-Splines plug-in for Rhino, or the Sub-d NURBS plugin for Modo or Max:

http://www.tsplines.com/subdtonurbs
http://npowersoftware.com/subdtonurbsoverviewmodo.html

- Michael