Whew, rcb and astromech, you're both making my head spin. The first Star Wars movie was the first chapter. There was never any intention to "start in the middle" nor was he holding back anything resembling the sequel movie plots for later. He had a single script, one that had several completely different drafts as he fine-tuned the story, but whatever he was working on was one story. And it wasn't a single story that contained the plots for what would later become ESB or ROTJ either. As someone mentioned earlier, only a few action sequences, like an asteroid chase and a wookiee battle were later reused in the sequels. But all this story about holding back episode numbers or having one big master script that was cut down into thirds is simply Lucas propoganda to make it look like he had the whole thing thought out from the beginning, which is simply not true in the least.