hoe do i get the pivot poit of a mesh?

hi, it is me again; i am having problems with blender python, the question is how can i get the pivot point of an mesh and how can i change this point, my idea is to rotate the mesh, but around a point that i decided.
Another question, how do i put the uv coordinates of an object like planar , spherical or the cilynders.
Another questiion how do i create an object like a plane without avoiding to make from zero.
i 'll trate to do it this way but nathing happens:
import Blender
obj=Blender.Object.New(‘Mesh’)
plano=Blender.Mesh(‘Plane’)
Blender.Redraw
but nothing just a point on th 3d window…
what can i do…