After seeing all the theory behind GT4, we're almost ready to start programming. However, you need to know Python to follow this tutorial.
Also, you need to be familiar with XML. You don't have to be an XML wizard, but should at least be able to read and interpret the different elements of an XML document. If you've never worked with XML, you should probably take a look at the following sites:W3Schools XML Tutorial : Tutorial that covers both the basics and the more advanced aspects of XML.
ZVON.org : Tons of XML resources. Includes some very good reference guides.