How to Print T-Shirts for Fun and Profit! (Paperback)
It is written by Scott Fresener who is one of the industry's leaders, and he also runs a screen printing school in AZ. Many of the other books I've seen are on a craft level, or talk about ways of doing things that are from the 70's and way out of date.
This book will give you a good overview of the whole process, equipment used and your options at several price levels (home made to large production), and even has plans to make your own press. It is a valuable resource that will save you lots of time and money. more details...