I'd probably recommend you just download Python from the official site, and configure Aptana to find it.
You can download the latest version of Python from here:
http://www.python.org/download/
You didn't specify whether you were using Python 2.x or Python 3.x? For compatibility reasons, I'd probably go with Python 2.x. The latest 64-bit Windows version of it is 2.7.2., direct link is:
http://www.python.org/ftp/python/2.7.2/python-2.7.2.amd64.msi
After you've downloaded and installed it, it will place your python interpreter in (assuming you use C:\ as your Windows drive):
C:\Python27\Python
You simply need to point Aptana to this. To do this, go into preference, then on the left, look for Pydev. Expand that, and look for the section Interpreter - Python
.

In theory, if you click Auto Config
, it should automatically detect C:\Python27. If it doesn't, you simply need to click New, then use the File dialog prompt to find C:\Python27\python.exe
. This will also automatically import all the Python libraries and site-packages you have installed as well (although if this is a fresh install, it'll just be the stdlibs).
Let us know if you have any issues with the above.
Cheers,
Victor