I just did this with crackdown, but unfortunately there were only 48/50 achievements :P Oh well I will try and get the 2 of them. Thank you so much losthope <3
Oh and for those of you wondering, I did this with an updated Xbox360, on Vista with Xsata.
P.S. If you're using vista and you keep on getting on getting the FATX error, try running Xplorer 360 as an Administrator. The same happened to me.