Try this:
>>> from pysphere.vi_task import VITask
>>> import pysphere.resources.VimService_services as VI
>>> from pysphere import VIServer
>>> server = VIServer()
>>> server.connect("1.1.1.1", "your_user", "your_password")
>>> vm = server.get_vm_by_name("Win 2008 R2") # get VM
>>> request = VI.Rename_TaskRequestMsg()
>>> _this = request.new__this(vm._mor)
>>> _this.set_attribute_type(vm._mor.get_attribute_type())
>>> request.set_element__this(_this)
>>> request.set_element_newName("Windows 2008 R2")
>>> task = server._proxy.Rename_Task(request)._returnval
>>> task = VITask(task, server)
Hope this helps