I'm assuming he's talking about the Black Knight. For the one who has its back to you at the bottom of the stairs, lure it all the way up to the open area where that locked door is. Just block him and back stab him. For the one at the top of the tower past the Hellkite dragon, keep him at the top of the tower. Do not let him push you down into the stairwell. Once again, block and back stab him.
Also, get the Drake sword: http://www.youtube.com/watch?v=lS0x5OpEt8M
And back stab >>>> parry