I'd like to think of God and Satan as the same power...If you like, God can be evil and the devil can be good. It probably doesn't make much sense to you but I think as reality is as grey as it is (and not black/white), then probably the higher power(s) are/is too. I honestly believe that thinking in terms of Devil/God is not very fertile thing to do. It easily leads to judging people to be totally good or totally evil, and that's evil i think.
Bas