hi
if your nurb model is created with several nurb patches assembled together then u can do 2 things..
1)before u assemble the patches assign to each patch a material and check "copy material and texture locally" at the window it appears when u execute the command "surf.mesh>assemble"
2)if u haven't applied materials before or checked this button u can always assign material to each subsurface the surface mesh is created from..simply select the subsurface u want and assign a material..(it's something like local materials in polygon meshes)..note that u can select only a subsurface and not a part of a subsurface..
Finally u can also assign a mix material to the surface mesh, using images (or anything else fills your needs) as the weight to control the blend or mix between multiple materials or textures..
I hope this helps a bit..
George