You always have to apply for a account.. Open means that they automaticly approves every application (including your dog�s... Othervise it isnt open...).
One thing though internal means that it is the devs/some other ppl who sit in a lan and test the game, external means testers over the internet.
Just in my honest opinion. If anyone has a beta/alpha terminology (sp?) book I would appriciate it.
C