If McCain had won the Republican nomination in 2000 (and if I'd gotten my friggin' absentee balot like I'd requested several months in advance), I probably would have voted for him as well. I didn't agree with him on everything (then again, I never agree with any politician on everything - there's always something we'll disagree on), but I thought he was a decent guy, and would make a capable president.
Charles Lewis's "The Buying Of The President 2004," which explains who's backing all of the presidential nominees, discusses the campaign and competiton between Bush and McCain.