Is Sephiroth actually Jenova?

[Mercen-X]

Now, I'll get back to the power of Jenova. These cells have an adverse affect on human cells, changing normal human cells into something more like Jenova cells. This grants humans some limited powers of Jenova, thus the reason for flying, walking on ceilings, and being unnaturally strong.

Wrong. No humans(injected with J-cells) can do that. Only Sephiroth(the real one) could fly, and only after he became Safer Sephiroth(and in the end of AC).

No.1 The flying Sephiroth was not the real Sephiroth. It was Jenova. The "real" Sephiroth is a corpse encased in Materia crystal.
No.2 I believe DM is referring to the part where Sephiroth is found in the materia because that is when CLOUD is hovering and walking around on the freaking ceiling. Hooah!

However, Cloud, in some fashion, it is never really explained, manages to get hold of the identity of his deceased friend Zack, and thus thinks he is Zack but with his own past. The two do not mix together very well, and I often refer to this confused Cloud as Zoud (it was better than 'Clack') to keep them straight..

Actually, I think that's fairly easy to explain. Both Cloud and Zack were placed in Mako pools at the same time. Since the liquid of the Lifestream does not need physical integration to communicate memories, Zack's life before the events that led to his death were telecommunicated to Cloud during their incarceration.

I need to correct myself. Cloud doesn't have Zack's memories. He doesn't remember Aerith. He doesn't remember Gongaga. He has Zack's personality as the Crystal has stated but not his memories.