CMake could not find the VTKConfig.cmake

When you have successfully built VTK you can give CMake a hint where to look for VTK with the VTK_DIR-parameter:

cmake -DVTK_DIR=/path/to/vtk/build-directory /path/to/your/source-directory

It seems like you just have the VTK source code but haven't built it yet. VTKConfig.cmake.in is a template used by CMake to generate the VTKConfig.cmake file in the build and install directory. Look at http://www.vtk.org/Wiki/VTK/Building to see how to build VTK.