Switch Edwards with Warner or Bayh and I could see this ticket winning, but Edwards will be an afterthought by 2008. He will be the Lieberman of the 2008 race, but weaker because he will have spent four years doing nothing noticable.
That is unless Edwards successfully challenges and takes Elizabeth Dole's Senate Seat in 2006, then it would only have been 2 years doing nothing noticeable and those would be the first 2 years rather than the latter 2 years.
NC has no US Senate race in 2006 (unless there's a sudden vacancy). Dole is up in 2008.