To reply to Phil Perkins concerns about Gamma et al: It's true that the Gamma book gives examples in C++ and Smalltalk, but this shouldn't be a problem. I don't know any Smalltalk, and I know very little of C++, but I am able read Gamma et al. without any problem. You hardly need to look at the code at all; you can understand the patterns very well just from reading the explanatory text.
Aside from that, the exam objectives explicitly name Gamma as the reference to study for Design Patterns. Quoting from the objectives:
"Patterns will belimited to those documented in Gamma et al. and named using the names given in that book....
State the name of a Gamma et al. design pattern given the UML diagram and/or a brief description of the pattern's functionality...."
That alone is reason enough to study from Gamma; if you know the pattern but call it by a name that is not given in Gamma, you'll run into trouble. The Gamma book is from 1995, so you should be able to find it in a library if you don't want to buy it. It's a pretty important book, worth the investment.
Read more about the objectives at
http://suned.sun.com/USA/certification/archobj.html