https://alliedplayaz.com/alliedplayaz/gt3/initial.html

a good tut on modeling a car with (the Porshe)NURBS.
modeling a car in NURBS is not patch modeling.

this is an intermediate tut, but for the most part he tries to explain things as clearly as he can.
as for the no hard edges on the viper, box modeling can give as good as result
assuming you have good poly modeling skills.
besides nurbs modeling is much more involved and time consuming than poly modeling.