Bush's primary win in 2000 came from the fact that he was able to get the Evangelical vote on his side pretty quickly and at the same time, get the big money donors to back him. The only wing of the party he left out were the Libertarian types, and they did not have nearly the amount of money and organization that they have now.
Bush would have issues with Romney and Huckabee stealing his thunder, not to mention his last name being a weight around him, as Conservatives do not like his father very much.
But I think he could win mainly because he was the best of both worlds, a guy who could appeal to the family value voters and the middle class business types at the same time. Now, if he was running in 2012 or 2016, different story entirely. I don't think he would do very well in either, as the Obama presidency aroused a libertarian fire in the GOP that he wouldn't do great at harnessing, seeing as Bush has always believed that government could be the answer to problems both foreign and domestic.
But in 2008? Pre Tea Party? I think he'd get it done after gaining some momentum.
Now, beating Barack Obama is a different story entirely, especially if the financial crisis goes OTL (which it likely would, no matter who was in office) with a Republican in the White House. But I think he could win the nomination.