so i opened halo 3 ODST and download the Halo Reach Beta and it finished downloading and all and i opened the Beta ASAP!! and i was able to play 1 match of it and it said 173,903 people playing or smthing like that!
After that game i could not play again as the servers crashed/ got overloaded :p.
more info from an official site not a fan :P http://www.examiner.com/x-13078-Xbox-360-Examiner~y2010m5d3-Halo-Reach-Beta-servers-overloaded