Hi
The user id and article are already associated (in #__cck_core as pk and pkb respectively ... ir is it the other way round, can’t remember off top of head??).
In afterstore the article would have been created.... so you can use $config(‘pk’) to get id of user and from there get the pkb from #__cck_core... though depends why you really need to relate the article id with the user id twice me thinks :)