This tutorial has no GT3 prerequisite documents, since it is intended as a starting point for GT3 programmers. However, you should already be familiar with Grid Computing. The following book can help you get up to speed: The Grid: Blueprint for a New Computing Infrastructure (Edited by Ian Foster and Carl Kesselman). Most of the book is easy to read and not too technical. It is also known as "The Grid Bible". With a name like that, you can assume it's worth taking a look at it :-) You might be even more interested in the second edition released in 2003, including tons of new material: The Grid 2: Blueprint for a New Computing Infrastructure (Edited by Ian Foster and Carl Kesselman)

You might also be interested in taking a look at the 'Publications' section in the Globus website, specially the documents listed below. However, these documents are rather technical and might be too hard for a beginner. You might want to just skim through them at first, and then reread them once you're familiar with GT3.