Q: I want to know the exact procedure, thanks.
A: buy a xbox microsoft points card.. or order the points online. Go to the Xbox Marketplace on your Dashboard and go to games, and then click on Rock Band. Or when you put the disk in theres A special menu right in the game that you can preview and download all the songs. just make sure to load your account with points first! Thats the legal way to do it. I dont know how to do it for free.