Are you sure you have set up the environment variables correctly? For example, be careful with quotation marks (otherwise do not put them).
VTK 7 Y (, , vtkpython ), :
C:\Users\lib>set PATH=Y:\VTK 7.0.0-RC2\bin;%PATH%
C:\Users\lib>set PYTHONPATH=Y:\VTK 7.0.0-RC2\bin\Lib\site-packages
C:\Users\lib>python -c "import vtk;print vtk.__file__;print vtk.vtkVersion().GetVTKVersion()"
Y:\VTK 7.0.0-RC2\bin\Lib\site-packages\vtk\__init__.pyc
7.0.0
C:\Program Files\VTK 6.3.0\bin\Lib\site-packages\vtk PATH ( DLL)