[kupoartist]

okies... as far as i can remember:

In a lot of ways, Zack is who Cloud believes he is, and the lives they lead individually are similar in some ways - Zack dated Aeris for instance, and Aeris is later intrigued as to why Cloud is so spookily similar to him.

Their paths come together at the Nibelheim Sephiroth incident: In reality, Sephiroth lead his group, consisting of Zack (a SOLDIER, First Class), Cloud (a bog standard Shinra guard) and another shinra soldier to the reactor. In Cloud's mind, he was Zack (or at least "SOLDIER, First Class"), and the travel-sick grunt was someone completely different.

When Sephiroth went beserk, Zack attempted to stop him, and failed. Cloud did however stop him, (despite having the masamune stuck in his chest) and Sephi was thrown into the lifestream. The wounds that both received were serious enough for them to get caught by the Shinra, and imprisoned in the Mansion's basement: from hereon, Cloud is a very confused thing, constantly blacking out, due to his wounds, and the experiments he is subject to (involving Jenova cells)

They then are able to escape, and head to Midgar. Shinra, catch up with both of them: Zack is shot several times over, and is certainly dead: Cloud survives however, and as he has already been dressed in Zack's uniform, he picks up the Buster Sword that Zack uses, and heads into midgar. He is then found by Tifa, at the Sector 7 station (the one the plate falls on... not sure if thats 7) and the game has effectivly begun, as he weaves the distant past of his own, with the recent and more glamorous close past of Zack's.

And that probably doesn't clear it up too much ^_^