Sounds like the download is bad for some reason. Redownload it, I guess. I would try the torrent if you used the mirror before... or the mirror if you used the torrent. I do not know what "bf2" is... so I am not sure what that means. (Sounds like you got to this point, but just FYI for others: The download either from torrent or from mirror will be some kind of an archive file, the torrent itself is a .dmg. If it is an .hqx, .sit or .zip you need Stuffit Expander latest version, which is free. If it is .dmg you need Disk Utility from the Application/Utilities folder to open it.)