I, perhaps, should have warned that the method does require some cost. Rhino, along with the T-Spline plug-in and a copy of ZBrush. It probably isn’t worth the investment unless it’s something that you need to use often.
If you search this forum, there are a few different posts about this type of workflow. There are a couple that have some very simplified step by step instructions, one of them is:
http://discourse.mcneel.com/t/help-converting-a-mesh-to-nurbs/17329/15
A YouTube search for “ZBrush ZRemesher” brings up a lot of videos from the ZBrush website and others that go into good detail of creating new meshes from various input files. A search for “ZBrush T-Splines” will bring up a few that show the whole process.