Hillary Clinton and Mitt Romney are in the same boat: they both were up in New Hampshire, and both thought they could win both Iowa and New Hampshire, and crush the field. Turns out, it didn't work that way, and they both lost Iowa by 9 points.
Hillary needs McCain to win New Hampshire to take Independents away from Obama so she can win. I would say that Obama is up around 4-5 points, well within the margin of error. Hillary's crowds look HUGE, which is always a good sign for her campaign.
Conversely, Romney needs Obama to win so that McCain will not have his Independents so that the Governor can win. I saw a peek into Romney's stump speech on CNN this morning and he was already presuming an Obama win, arguing that he would be a better change agent than McCain, who he argued had been the Senate for too many decades and too old to go up against that whippersnapper. Then he said "or it could be Hillary. I would can't wait to meet Hillary face to face." That was the biggest applause line.
Of course, the one Republican that Obama has matchup problems with is John McCain (currently he cleans the clock of Giuliani, Huckabee, and Romney). So while Clinton could still win the nomination even if she loses NH, SC, and NV (because of her overall delegate count), it could be short sided if Obama manages to create a real bandwagon effect.
Similarly, Hillary's presence of the ticket is the best thing for Republicans in terms of exciting their base given that their base is really not that into their field. And currently, the weakest Republican in swing states against the Democrat's top three is Romney. By contrast, McCain is the strongest against the Democratic field (although he loses to Clinton and Edwards and is close to Obama)
Perhaps the long term interests of the Democratic and Republican parties and the short term interests of Clinton and Romney might be at cross purposes.
PS, I wish I was up in New Hampshire right now. I remember freezing my butt off in the Granite state weekend after weekend, holding up signs, going to rallies, and meeting voters. It really is fun and exciting. I would recommend anyone to get involved in a campaign some time.