I think he can take Hillary. It's not a sure thing. Even though 50% of all Americans don't like Hillary, she is still a formidable candidate. And there are lots of people (mostly Republicans) who don't like John McCain, but I don't see that as a final bar to his candidacy. Anyway, the two of them are both Baby Boomers, and we know them from of old. I see Hillary vs. McCain right now as an even matchup.
McCain vs. Obama is another thing. Personally, I see Obama as just a more likable Hillary. He's still all leftist policies and hot air, just like her; but he's also young and fresh. He excites people (especially people who think in terms of personality, rather than policy). Against McCain, he would look to many politicos as an utter lightweight; however, standing on the same stage with each other, Obama would make McCain look older than dirt and only half as attractive.
In any case, the GOP is going to have to run a near flawless campaign. And that means that the various disgruntled factions within it are just going to have to Suck. It. Up. and get with the program. I don't know the personal relations between McCain and Huckabee, but Huck's looking more and more Vice-Presidential by the minute.
What's really different about this campaign is that this is the first election since 1952 that a sitting President or Vice-President isn't on the ticket of either party. It's an open seat, so to speak. (The closest either party has to a candidate-in-waiting is Hillary, the former "co-president" whose only foray into policy back then was an utter botch, but who now takes credit for everything that anybody did that was good back when.)