In the Sarah Connor Chronicles, why did they time leap from 1999 to 2007?

I'm a little confused about this. I thought the Sarah Connor Chronicles took place between Terminator 2: Judgment Day and Terminator 3: Rise of the Machines. Doesn't Terminator 3 take place in 2003, in which the war between man vs. machine begins? If they time leaped forward into 2007, it's as if Terminator 3 didn't happen. Can someone explain this to me?