Just recently, an article was posted over at http://www.bungie.net , with quite a helping of news.

The news, finally, concerns the Beta's release date, and also brings a new Vidoc with it. Just like the previous vidocs, this one was actually created months prior to it's releasal. The Vidoc shows off some of the new things in Halo3, including new weapons, new functions, new items, aswell as a new weapon class.

The "X" button, as some of you may know, has left quite a few theories across the internet. It's also been revealed that the "X" button is used for the new equipment the chief carries. The confirmed pieces of equipment he can carry, besides the grenades, are Bubble shields, Portable Grav lifts, and Trip Mines.

The Halo3 Beta will be released May 16th, and will run for roughly 3 weeks. In the Beta, you will be able to play all of the new gametypes they've introduced, aswell as all of the old. The Beta will not showcase all of the weapons, abilities, items, and multiplayer functions, but will show off quite alot.

The graphics in the Beta, will represent most of what the game will look like in it's final form. To date, only Alpha screens have been shown off.

http://www.bungie.net/News/ content.aspx?type=topnews&link=MPBetaAndVidocRelease