you can use getmac. see getmac /? for more info.
Also: I think that tool would be available via a resource kit for W2K and earlier (it's included in XP Pro and up). (just checked, it's in the NT4 resource kit and no doubt is in the w2k one). I doubt they are running an OS before XP on any of the machines anyways, though.
The batch method will work with NT4 and 2000 (not as sure about NT4).
getmac would be the better solution regardless- it's designed for the very purpose required.