the difference is the hardware units that run them.
the software is basically the same. you have to understand that up until recently Digi made their own gear and sold it with their own software. So before, you're only choices were Mbox, 002 and 001. Within the past few months, Avid aquired M-Audio and decided to make most of their hardware units compatible with pro tools too...and they just decided to call it M-Powered. So this is why there are two different (but same) versions of software. Both are completely compatible with eachother. The only real difference is M-Powered you have to buy separately while Pro Tools comes with the Mbox.
decide on which hardware you like and buy that one.