1) You should never care what the python interpreter does. It is not the same as running a python program, and in my opinion it is useless. Instead, type your code into a file named my_prog.py, and run it:
$ python my_prog.py
2) You should never care what IDLE does because it is the worst text editor imaginable. Your mac comes with vim, which you can learn how to use by doing:
$ vimtutor
Once you've learned the basics, you can upgrade and install macvim, and something like the vivid chalk color scheme, for a real sharp looking editor. There are also thousands of useful plugins you can employ with macvim. You can search google for the "best of the macvim plugins" and see which ones you might want.
3) Why do you use macports to install modules? You can download the module, then untar it:
.../Downloads$ tar xfvz some-name.tar.gz
then cd into the newly created directory:
.../Downloads$ cd some-name
then read the README or INSTALL file for the directions on how to install the module, however typically all you do is:
.../Downloads/some-name$ sudo python setup.py install
That will install the python module in the default location, which is not /opt/local on my mac; it's:
/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
You shouldn't need macports for something so trivial.
4) It looks like other people have had problems with IDLE when installing modules in non-standard locations, so you might want to search google and see if you can find a solution there: e.g. http://ubuntuforums.org/showthread.php?t=253555