If Romney wins Iowa and NH but Newt or Perry wins SC then it is going to be a long slog to the nomination more than likely however if Romney sweeps all three it is pretty much game over. Even if Romney has a close 2nd he will be formidable since Nevada will likely go his way. Not sure how Florida is looking but Michigan would be his as well. This is also where money and organization start to pay off which Newt is sorely lacking. In any event if Romney wins Iowa he will be in a good position to win the nomination.
Nobody, to my knowledge, has ever won SC without winning either IA or NH