Successfully installed it on a friend's computer. He was able to install it completely on both his XP laptop and his Vista Desktop (though the sound was screwed up, thank you Vista)
Although he said that he had a similar "99% install" problem with ReAct and couldn't remember the solution. Figures.
Anyway, it's probably something that happens one in a billion times or something. I'll look into a bit more. If anyone finds the solution let me know.