How to install PyQt5 on Windows?
Mainly I use the following command under the cmd
pip install pyqt5
And it works with no problem!
The easiest way to install PyQt is to just use the installer (Link in your answer, step #5). If you install python 3.3, the installer will add all of the PyQt5 extras to that python installation automatically. You won't need to do any compiling (none of: nmake, nmake install, python configure).
All of the build options are available for if you need a custom install (for instance, using a different version of python, where there isn't an installer provided by riverbank computing).
If you do need to compile your own version of PyQt5, the steps (as you have found) are here, but assume you have python and a compiler installed and in your path. The installed and in your path have been where you have been running into trouble it seems. I'd recommend using the installer version, but you need to install python 3.3 first.