I summoned Solaire to help with the Ornstein and Smough fight. Between the two of us, we worked both of their HPs down before he died. Then I concentrated on Ornstein first. I was using Quellag's Fury Sword since I went with a pyromancer build. I don't remember what armor or rings I was wearing. Once Ornstein was dead, I switched to an upgraded fire longbow and just did the old 'hit and run' on Smough until he died. And yes, I died a lot trying to beat those guys.
Damn, y'all are making me want to get back to that game, now. Last I played of it, I was dying to those big skeleton dogs.