You need to select each of of your NURBs surfaces, and under the attribute editor for each surface you'll see 'Tessellation'. Select 'Highest quality', and bump up U and V divisions factor to the highest it will go. This will increase render times, but sort out those dodgy NURBs surfaces when you render. A good way to see the difference this makes is to extrude a circle along a curve. Render it at low res tessellation - the cyclinder will be jagged. Increase the tessellation quality, and it will render out nice and smoothly.
Hope this helps