Can be MAX and AutoCAD 3D files converted to NURBS ?
Yes, but the only program i can think that does it is maya.
You import your polygon model, you select it and you convert it to subdivs
(modify/convert/polygon to subdivs). After that you select your subdiv model and convert it to nurbs. (modify/convert/subdivs to nurbs). Easy and with great results. The only problem is importing and exporting is not very straitforward in maya.