I personally think Kerry was more of a problem than Edwards. It wasn't Edwards's fault that Kerry couldn't make up his mind on the war, it wasn't Edward's fault that Kerry had huge descrepencies and flip-flops within his Senate record, and it isn't Edwards's fault that the Democratic party hasn't yet learned that New England senators make for terrible presidential candidates.
I for one think the ticket could have been far better had it been backwards with Edwards on top and Kerry as the VP. I know a lot of people that said they liked Edwards, but not enough to vote for Kerry.
Yes, I think that an Edwards/Kerry ticket would have beaten Bush/Cheney. Edwards would have been able to win Ohio, I believe, and perhaps also some other swing states.