The moment beta 1 was released with version 5112, the code tree for beta 1 stopped and all code moved into the beta 2 tree. Since beta 2 isn't officially released yet, 5219 is post beta 1 and pre beta 2.
Under my MSDN Academic Alliance subscription, I have access to the vista beta 1 release but not the 5219 version. Is this correct? Is it restricted to certain types of subscriptions and why? How can I obtain this build 5219?