Kerry is not appealing to the MTV crowd or really any other crowd either. His approval rate is only as high as it is because people are unhappy with Bush and have no other realistic options besides Kerry.
I don't think Hillary wants to be part of an administration that would win the presidential election (it could happen) based on the fact that nobody likes the other candidate. I think she wants to win based on her ideals and her own platform. I also don't see Hillary running as a VP anyway. I think she wants to be the big cheese. I could be totally wrong. This is just my speculation. Based on the way that Kerry is running his campaign though, if enough people start saying it is a good idea, he will probably ask her.