Installed additional python2.7 to Snow Leopard. What happens to modules I want to install?

Question

I recently asked if I should upgrade python 2.6 to python 2.71 on my Mac (Snow Leopard). I was told to install 2.7 without removing 2.6. Done!

Now I was wondering how the installation of new modules is handled:

Does both 2.6 and 2.7 access the same place where all new python modules are installed by pip, easy_install and setup.py? Is there something I have to take care of?

Another question occured to me: How do I tell a script that I have written to be run by python 2.7.2?