Ed Davis did a lot of research and came up with these four web pages as being the best place to start understanding what the VA can do and how to get them to do it.
He was kind enough to share them. They really are complete. Read all four.
http://www.yourvabenefits.org/
http://www.aarp.org/health/conditions-treatments/info-04-2010/giving-back-to-vet\ s.html
http://www.vva.org/Guides/AgentOrangeGuide.pdf