IREX is hard
Bob Tait does a very good IREX book. His CPL Law was pretty good, too. I self-studied both, and passed both first time.
IREX was almost as hard as all seven CPL exams put together. (Ensure all your DAP's are up to date). There are books and CD's containing nothing but practice exams, which are very useful.
Hope that helps.
DIVOSH!