The call in the explanation doesn't give all memers of the group - members of a group G1 which is itself a member of a group G are automatically members of G, but will not be listed by calling xp_login 'G', 'members'. So one has to recurse down the tree to get all members of G. There was a connect item about this a while back, closed as "won't fix".
The AD Users and Computers tool has the same problem - it doesn't recurse.
So in effect there isn't any means of getting all the members of a group by a simple xp call, you have to provide the recursion yourself.. Unfortunately I misunderstood the question as asking for that, so I got it wrong.