Convert Mesh to Curves

Hi guys,

I already have some experiance with Autodesk Maya. But now i try to get started with Blender. During work some of my pieces got very large and i thought about the possiblility of converting them to nurbs to increase the performance. With large i mean files with 500mb meshes.

Though i dont know if this method will solve my problem i would like to try it.
Unfortunalty it seem that converting from a mesh is not as simple as vice versa.