Either version is fine, its just for some specific functions that there will be different ways to code it.
And your specs barely matter, python doesn't really need much ram at all, well at least on Mac, which is on what I tried it, it doesn't seem to need much power to work well.
If you have Mac OS X you already have a version of it on your terminal (it will tell which version you have, too. For exemple I'm using mac OS X 5.8 and I have python 2.5.1). Just boot up the terminal and type python in.
Otherwise, there are two main versions: 2.7.2 and 3.2.2. Due to the VERY SMALL difference in coding (seriously you can easily change and fix the files just to make older files work on the new one and vice verso), some files will work on a version and not on another, so I recommand perhaps having both versions available on your computer.
Python is totaly free, works both on Windows XP/Vista/7 and Mac OS X (and I think on Linux too), and can be downloaded on Python's website.
Here: http://www.python.org/getit/