Confusion over Cloud (Spoilers ensue)

Okay so it's my first play-through of the game (I'm very lazy and somehow put off playing the game for years) and I'm quite confused over a few things...

I understand the whole thing about Cloud actually being one of the soldiers present (not actually a SOLDIER though) during the Nibelheim thing, and I even understand the part where Cloud goes after Sephiroth and gets stabbed in the freaking chest...but here's where I'm lost:

So the people of Nibel were then used for Hojo's experiments, and Cloud was made as a clone of Sephiroth? Now, do they mean clone as in Jenova+Mako enhanced, or clone as in...cloning sheep. Because Cloud certainly doesn't look like Sephiroth. And another thing...does this mean that the Cloud we know and use throughout the game isn't actually his original body? Or was his original body salvaged somehow with the "cloning" thing? I figure a stab woulda killed him...and so its almost like he's brought back from the dead...

Now that I think about it, the Vincent thing was similar...he was SHOT and then made into what he is...

I also don't really get the mechanics of Tifa's/Cloud's momories and what Cloud should and shouldn't know (that whole dialogue went right over my head)...but whatever. What I'd really like to know is what you veterans know of the plot in the areas I described.

Okay, it's a bit confusing but here it goes.

Clone deal - By clone they mean Jenova+Mako enhanced, not the sheep sort. Most especially because, if Cloud was a clone in that sense, he would have looked exactly like Sephiroth. Clone was actually a pretty poor word. What happened was, Cloud and Zach were taken and put in the tubes in the basement of Shin Ra mansion (this is a cut scene you may have missed, go down and examine the tubes if you havent already). Cloud wasnt killed, just wounded.

Tifa's memories... well, Tifa is handling Cloud with kid gloves throughout the game. She senses something is up, but she doesnt know what, and she doesnt come right out and say that she knows Cloud's memories arent right. Instead she gently steers him in the right direction... it's very possible that if she had come right out and corrected him, he would have either denied it or lost his mind. What Cloud should and shouldnt know, he probably makes it up as he goes along (that voice in his head helps) and he probably talked a lot with Zach, so he got the basics on that guy. Obviously he didnt know everything Zach knew (or else he would have known Aerith).

And if I'm right in remembering (it's been a while) isnt it Sephy that gets stabbed in the chest, not Cloud?

Cloud does get stabbed in the chest. He then swings Sephiroth by it into the Lifestream.

Oh that's right. Been a long time... thanks.

Cloud slashed Sephiroth in Jenova's chamber; later, Sephiroth stabbed Cloud through the shoulder, and this act of 'bad aim' allowed Cloud to gain the upper hand.

Ahh thanks guys...it's all comin together now =)