In addition to what Henry has already said, which I concur with, here's some info from the Hardwood Organization on How To Refinish A Staircase. You will read that it's not that much different from refinishing a hardwood floor.
If you have more ?'s, do post up. Perhaps a new post would be better as this one is already getting 'buried'. And as usual, please give as much useful info as you can.