You cant...
Well, you can pull out the hard drive of the PS3 and pop it into a SATA 2.5" external enclosure. Format the drive, and then back stuff up... But this cripples the PS3.
not if you partition it
It is not meant to back up computer files......You can transfer compatible movie files to it, music, pictures.i dont get it. whats the point of the 250 gig hd if i cant put stuff on it? there has to be a way to do this.
I think he went and bought a PS3, not just the hard drive...Wait, so you're saying you went out to the store, bought a PS3 Hard Drive, trying to use it as an External Hard Drive, and don't even have a PS3? FAIL!