I just finished watching the commentary, and this is the story as i gathered it from the timeline in the credits:
Cortez did not put the curse on the treasure, the heathen priest god cursed it, because he gave the treasure to cortez to try to quell his gold lust. The curse was that if any took any of the gold, he would be undead.
Jack knew about the curse before he took on Barbossa and the mutineers onto his ship at Tortuga(one of them being boot strap bill), but Jack did not believe in it, thus the refernece later when twigg and the other man break into the prison: "So there is a curse. That's interesting."
He told his crew(the one that later marrooned him on he island about the curse and the treasure, and the island that no one can find except if he already knew where it was. They also did not believe in the curse, but Jack had been to the island, and told them that the treasure was real enough. This awakend the lust for gold, and in answer to a question, Jack already knew where the secret island was, and in answer to a question he gave up the bearings of the island. Now that they knew where the treasure was, they had no need of Jack so they marooned him on the rum runners' island, and set off to find the treasure. Boot Strap did not assist in the marroning, but he stayed with the mutineers on the ship. When they reached the island, they all took the gold until there was nothing left in the chest, and they spent it as they would ordinary treasure. They learned from their experiences that they couldn't feel anything, or die. They also learned that ALL the treasure had to be replaced for the curse to be lifted. Boot Strap was angry at Barbossa for marooning Jack, so he told them they deserved to be cursed, and that they should remain that way always. So he sent one piece of the treasure to his son for safekeeping, so the pirates would remain cursed.
Barbossa got really angry ar him and strapped him to a cannon and threw him overboard. This is important: when i think his name is pinnel? tells that the last he saw of old boot strap, he was sinking down to the crushing black oblivion of davy jones locker. Now although he was cursed, and coudn't die, so he was still alive, they were implying that he went so far down there would not be much left of him. Then after that they learned again that they neede turner's blood to lift the curse. These are the events leading up to the movie. Make sense?