According to Kotaku, the PS3 version of Final Fantasy XIII has freezing issues. This problem was reported by a few people on various forums and, as you can see, seems to occur in the first chapter of the game (and at other random places too).
Not many copies suffer from this issue but nevertheless it would be nice if Square Enix provides us with a solution for this annoying bug as soon as possible. This post will be updated when a solution/patch is available. If you’re experiencing this problem I’d advise you to try again with a new save file (or trade it for a new copy if possible).