Do you know if its possible that the Halo Reach beta will be able to be extracted to an .iso file when it comes out?
From what I know it won't be on a disc but rather something that'll be downloaded from XBL and even if it were on the disc it probably wouldn't be playable unless it was a JTAG console, thought this is just a guess.
My theory is that it will be like the Halo 3 beta that you could obtain with Crackdown, you will need need the Halo 3 ODST disc in to download / play the beta. Again just a theory but anyone who owns ODST can download the beta when its out.
Most likely it will just be the multiplayer beta. I doubt that there will be single player demo. Doesn't sound like the beta will be exclusive to the ODST disc it is downloaded from. I preferred the way the Halo 3 beta worked where you had to load up Crackdown and play it from there; made the beta more exclusive.
Multiplayer Beta will be enabled from the ODST disk. I didn't get a chance to play the 3 beta, but my guess is that it will be a program downloaded to the 360, but you can only access it from the menu on the ODST disk.