Well movies backed up or not will play just fine with a modded and normal console so thats not a good way to tell.
But if the flash went successfully and the dvd drive still plays original games as well as dvd movies then it should play your backup games just fine.

i have the same problem i flashed my drive with the same stuff as the "Elminster_BR" but afterwards i cant play original xbox games but i can play 360 games. when i flashed my xbox 360 drive it sayed it flashed it succesfully but my original xbox games wont work.
...........................any ideas or help would be appreciated..................................................