The IADsGroup interface has an IADsGroup::IsMember method. This method returns TRUE if the specified object is a direct member of the group, that is, the group's member property contains the specified object.
Note A group can contain other groups (nesting). The IADsGroup::IsMember method does not recursively check the member properties of groups in its member property, groups within those groups, and so on. To recursively check if an object is a member of a group, you must enumerate the groups in the member property, check the members of those groups to see if the object is a member, and if those groups contain other groups, check their members, and so on.