If the widget is a subclass of GtkMisc, use its methods to set the alignment. Otherwise pack it to a GtkAlignment. In both cases it has to be attached to the table with vertical GTK_FILL flag.
Thanks for the fast anwser :) The widget is a box, prefilled with some other widgets & some logic, so I used the Alignment. It works fine :) Do you know hat the Gtk AnchorType enum is actually used for? Jonathan