Microsoft owns the publishing rights to ME1, so it's doubtful it will ever end up on the PS3. The upcoming PS3 release of ME2, however, will be coming with a sort of interactive digital comic that will apparently allow new players to make some of the major decisions that were presented in ME1.
As for backwards compatibility, as far as I know all current models do not have it. The original PS3s shipped with both the Cell processor and the Emotion Engine chip (which was the PS2's processor), but then they switched to software emulation because it was cheaper, and then finally they removed backward compatibility completely.