Do you think Gore could win in 2008? I don't.
Edwards would have been in a close race for senate re-election, you can't definitely say that he would have lost it.
I think it will be Hillary, but if she doesn't run, Gore could probably take it.
Edwards would have been the underdog, and it is very doubtful he could deliver NC to Kerry. Clark would have a better chance with Arkansas if Kerry chooses him.
Bush will lose at most one Southern state in a 50/50 election, and Bush will only lose one if Kerry has a Southern on the ticket. Trying to win Ark with Clark or NC with Edwards is not worth the risk. IMO