I don't know how many democrat votes' he can win over (Here, i'm talking about the disenfranchised Clinton supporters) due to having a woman VP. Many people (sadly) still vote along party lines, and to them, a republican is a republican. Even with Obama's choice of Biden (did he offer it to Clinton, and if he did, did she turn him down?) for a running mate, Obama's not going to lose any voters from the Democrat side of the isle, IMO. He might pick some up, with a(n) older white male seeming to anchor his presidency, to many, keeping it from being too liberal.
Don't get me wrong, this won't win very many republican supporters' away from McCain, even with a woman VP. I think that this election, you might see a strong showing for independents.
Independents will decide this election, for sure.
I truly don't think Obama offered the position to Clinton. Earlier in the campaign, I think it was a sure thing. The Clintons, in going for the throat, made that an impossibility. Bill, more than Hillary, IMO, made her blacklisted on the ticket to Obama.
I will say this, Biden and Palin debating will not be a thing which will help McCain's cause. He's seriously in the grips of dementia if he thinks she will carry such a debate. Her learning curve on foreing policy and economics is incredibly steep.
In the end, the VP choice only really affects McCain. (he's 72 today...) I don't think he's
gaining any support with his choice, only making those who were voting for him anyway, feel just a little more "comfortable".