The good news is that it's not really that tough to learn both Python 2.x and 3.x. You can install the latest 2.x version as the version registered with the system to run Python scripts by default, but also install the latest 3.x version to explicitly kick off when you want to. That's what I have on my Windows Vista system.
Then, the key document for learning the differences between the 2.x and 3.x versions is:
http://docs.python.org/3.1/whatsnew/3.0.html
If you read Python learning materials out there which are based on 2.x and also refer to that "What’s New In Python 3.0" link above, you'll get an understanding of how things changed. Also see the other whats new docs, like for the differences between 3.0 and 3.1, but the link above is the main one to understand the 2.x vs. 3.x changes.
