What does Python Launcher do

There are several ways to install Python and which way affects the later answers. In all cases you should install a later Python 3 version - 3.1.3 is the latest released version. For choosing which to run I would call python3.1 or python2.6 to be explicit as the language differs enough that the code is specific to the 2.x or 3.x branches. In fact much code starts with the #!/usr/bin/env python line but is 2.x specific. I would say that having the python executable on your path being linked to python3.1 would be a problem Apple scripts that use python always look for /usr/bin/python so will always find the Apple version and not a properly installed other version.

easy_install is from an external package setuptools and you can tell setup.py where to put it.

Simplest is install from the python.org installer This will give a python3 executable in /usr/local/bin (and possibly python as well). In this case I would create a python symbolic link in ~/bin (pointing to the apple python or python3 and you can switch where it points as you require without sudo which a link in /usr/local/bin would require.
In this case I think easy_install for python3 will by default end up in /usr/local/bin and the apple one is in /usr/bin

I use macports versions and they install in /opt/local and have a script port select that will switch /opt/local/bin/python between the 3.1 or 2.6 versions (or any others you have installed) - unfortunately not does not do this for easy_install which is in /opt/local/Library/Frameworks/Python.framework/Versions/2.6/bin (or 3.1 etc)

IDLE requires TK to work. You need the tkinter package for your version of python in order for IDLE to work. You probably want py27-tkinter and py32-tkinter. Unfortunately, you'll probably have to go with the default xll version, the +quartz variant is not well maintained upstream. It won't build in x64 on Lion+ or with Xcode 4.4+ because it uses deprecated QuickDraw APIs which don't exist in the 10.7+ SDKs. Xcode no longer includes a 10.6 SDK, but you might be able to get it to work on 10.6.

https://trac.macports.org/ticket/32329