I use the Python 2.7.3 that comes with Softimage 2015 SP1, but I do also have Python 2.7 installed on my system.

1. Download and install PyQt.
2. Set the PYTHONPATH environment variable to point to the location of PyQt4. You could do this in setenv.bat, or in the System environment variables. In my case, I set it in setenv.bat to point to C:\Python27\Lib\site-packages, which is where I installed PyQt.
3. Download and install the PyQtForSoftimage addon.
4. Check that everything is working. Open the Plug-in Manager, find PyQtForSoftimage, and run some of the examples.