So, I tried installing PyInstaller in my Python 3.4 dir but, for some reason, I've been getting errors and I'm not able to install it. I however, do have a working PyInstaller in my Python 2.7 dir. I need to compile an executable for a Python 3 script. So I was wondering if PyInstaller from Python 2.7 can do that for me?

The default version of PyInstaller only works with Python 2, so no, you cannot use it with a Python 3 script. However, there is an experimental version with Py3 support on Github, so you can try that if you wish.