As for the dragon, here's what I always do - stand on the bridge and take cover on the LEFT side, pressing against the stone -| |- like so. Pressing against the stone! That's the only place your safe from the fire attack. Then wait. Just wait.
Eventually, the Dragon will get fed up with your shit and leap down onto the bridge. At this point you haul ass, bolt across the bridge running underneath it, stopping to loot those 2 corpses for the Claymore and a Large Undead Soul(IIRC?) if your feeling brave. Then dive behind the rock on the left side again. Wait for the dragon to finish spamming fire at you, it'll march towards you. Then, bolt inside the room and take cover out of the dragons LOS. Wait for it to re-perch on the castle, kindle the bonfire and pull the lever. Viola.
Eventually, the Dragon will get fed up with your shit and leap down onto the bridge. At this point you haul ass, bolt across the bridge running underneath it, stopping to loot those 2 corpses for the Claymore and a Large Undead Soul(IIRC?) if your feeling brave. Then dive behind the rock on the left side again. Wait for the dragon to finish spamming fire at you, it'll march towards you. Then, bolt inside the room and take cover out of the dragons LOS. Wait for it to re-perch on the castle, kindle the bonfire and pull the lever. Viola.