I don't know how you're populating the data in listbox2, but if you use the SQL statement as your listbox2.rowsourcetype you could call the listbox2.requery method from the listbox1.interactivechange method and pass the parameters to the SELECT statement with listbox1.value. This would allow you to update listbox2 with the pertinent data whenever a new selection is made in listbox1.
Life's short, have fun!
Dan Madero