Sayid didn't change anything. Whatever happened, happened. The only one who can change time is Desmond.
Sayid was one of the first ones to meet Ben (I can't remember who found him in the parachute... was it him?). It'd be interesting to watch that scene again and see if he drops any clues.
Yeah, Sayid was the one who found Ben. Sayid was with Rousseau at the time.
