I had the same problem. Once I spent half an hour on this battle and lost at the very end...grr. I eventually just had to reload an earlier file and level up. Quistis' Mighty Guard comes in REALLY handy, but make sure she's at really low HP because then it'll cast not just Protect and Shell, but also Haste, Float, Regen, and Aura. Then, just whack away with limit breaks. Try to get Squall's Lionheart, it works wonders. If you can't do that, though, Aura magic (draw from Seifer) and Haste can work wonders. If necessary, use some Full-Lifes. If you have the Phoenix Pinion, I think you can use it (I think it will hit Rinoa though) and he might save your butt more than once after that...Good luck with this nasty!