To the best of my knowledge, he was leaning against it, and was hinting that they might support the democratic party, but I know he did not confirm he wouldn't run, and the green party has not said they wouldn't put up a canidate (you have to remember, Nader won a primary against bigger kooks then him).
My feeling, if they nominate somone like Kerry or Dean, or one of the ultra liberal guys, they won't run, or they will put up a false canidate who's sole job will to register voters, and attack republicans, and will only try and draw votes in safe dem states.
If the canidate is Joe Lieberman, Nader will definatley run, and they will fight all the way against holy joe, they hate him more then the freepers do.