Barbara Heidenreich has a good book about training for fearful and/or aggressive birds. I have seen her at work and she's a master. The book is called
The Parrot Problem Solver, (available here:
http://www.goodbirdinc.com , as well as other sites.)
Also, Dr. Susan Friedman has a group on Yahoo called ParrotBAS in which her students work one on one with parrot owners on behavioral problems. It's a fantastic resource.
ParrotBAS
What they teach is truly "state of the art" in terms of parrot behavior and training, and they have many years of experience consulting with zoos, training many different kinds of animals, and teaching.
raz