that he's gonna take Giuliani at the NYC convention. It would be a popular choice with the moderates and the middle, and even some democrats, possibly, but Giuliani's pro-choice, gay friendly positions would not play well with Bush's conservative Christian base.
Also, he had that messy divorce, and he got spanked a bit by the 9/11 commission, and people's fond memories of him are as vivid as they were 3 years ago. And despite the fact he was mayor of NYC, he hasn't ever held an elected national office.
I don't know about McCain. I know he'd like to be President, and VP certainly sets on up for that, but he also likes being the independent maverick, and he'd have to give that up for 8 years to be VP. Plus he'd have to swallow some pride after what Bush did to him in South Carolina in 2000.
Same goes for Powell, he's already chafing as Sec of State. How badly does he want to be President? I don't think that badly.