bungie.net have posted a Halo 3 Beta FAQ. Some of the more interesting Qs & As are:
When does the beta start?
The beta will not start when Crackdown is released. The beta will go live when it’s ready, which should be sometime this Spring. The team is currently busy whipping the included content into shape. Our goal is to deliver a fun, solid game experience though it will still very much be a “beta
How long will the beta last?
The beta will only be playable for a limited time. Exact timing is still TBD.
How many players are going to be in the beta?
A lot, many thousands. Let's just say, you won't have trouble finding a match.
Will we all have to sign NDAs and never speak of the beta? Will you try to contain screenshots and movies coming out of the beta?
Nope. In a perfect world, maybe, but it's hard enough when the participants are just a few thousand MS employees, let alone thousands and thousands of Halo fans. We don't expect anything in the beta to remain a secret. The beta will be covered by a normal user agreement, with lots of caveats about the fact that it's not finished, only lasts for a short time and so on.
full FAQ
in other Halo news, Bungie have released this teaser image:
Note: Fall 2007
