As asmeurer said, when in your py3k environment on the command line you can start the 3.4 kernel using the ipython notebook command. You can run both 2.7 and 3.4 at the same time if you specify a different port, for example ipython notebook --port 8080 . 2.7 by default will be 8888.
Note that by default, IPython will look in your current directory for laptops and store them there if you create them, so it may be useful to create a directory for Python 3 laptops only and either cd to it before starting it, or specify a directory with ipython notebook --port 8080 --notebook-dir C:\\Users\\[User name]\\Documents\\ipython3notebooks
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