is it right, that you want the items displayed as table inside the _poped up_ combobox? I just consulted the API and as i understand it, the renderer (which would have been the one to use) and the editor both are only applied to the ComboBoxField. that is, i'd say, the field you see any time (a JTextField as it seems).
if you just want to display more than one value in one row without the looks of a JTable then
you should implement this feature in your ComboBoxModel.
if you want to really have a jtable inside a combobox (and not just one tablerow after another) then you will have to take a closer look at the ComboBoxUI and its subclasses. look for the popup of the combobox (something like createPopup()).
have fun
chantal