If Enron's demise was fueled by unmitigated greed, then the undoing of AOL Time Warner was powered by the giant egos and self-righteousness of its chiefs: Steve Case and Gerald Levin. Eminently enjoyable, ''Fools'' is a gossipy, in-depth look at a deal doomed from the start. Rarely were two corporate cultures so badly mismatched: ''It was like trying to mate a horse with a dog,'' said one participant. Time Warner execs were appalled by AOL's casual attitude. (''They think e-mail is about beer bashes at five.'') AOLers found Time Warner's elite uptight and ''obstinate.'' (Warner Bros. refused to procure Mel Gibson to record AOL's ''You've Got Mail'' messages.) Case and Levin wanted the megamerger to define their careers. Munk, a former writer at FORTUNE (which, like EW, is part of Time Warner), admirably shows that they may have gotten their wish.