A bug has been discovered that sometimes results in improper text display. Basically, you won't see any text at all. If you encounter this issue, you can fix it yourself by doing the following.
1. Restart your Xbox 360
2. Boot up the Halo 3 Beta
3. While the Halo 3 Beta is loading, immediately press up on the D-Pad and hold the A button until you see the Bungie logo. If you perform this correctly a dialog box will appear confirming maintenance has been done to your system.
4. Resume the Halo 3 Beta!