It doesn't have AF-S focusing and with the weaker camera focusing motors like the one in the D100, the AF will have a hard time keeping up with subjects moving quickly toward or away from you. Having the stronger AF motor like the one in the D1 series (or F5 and F100 bodies) helps. I also suggest using the AF limit switch, this will substantially reduce hunting when the camera doesn't lock focus. You have to pick your working range ahead of time, but it is well worth it in my experience.
If you limit your action photography to panning where the subject isn't rapidly coming directly toward or away from you, the AF can be used with success. AF isn't overrated for action photography, but if you want to use AF for fast action you need a fast, AF-S lens. The 80-400 isn't that lens.