Crowley has the McCain/O'Reilly transcript where the senator denies voting against Bush in 2000 here. And Mike notes that either McCain or Arianna Huffington is lying. According to Mickey Kaus' math, it is actually now 4 people who say they heard McCain make the comment.
Even better than the transcript, however, is the video itself. Not only does McCain make a (Freudian?) slip, but he seems, er, unconvincing. The time counts down from around 7 minutes. The crucial section starts with about 1:10 remaining. You can wtach it here.
--Isaac Chotiner