Did you try coffeeshop's code?
The technique you are refreeing to is called "Cascading Lists"
The technique is basically the same for Comboboxes and Listboxes.
Here are some great Tutorials:
http://www.fontstuff.com/access/acctut10.htmOne table
http://www.candace-tripp.com/download/cascadecombo2k.zipTwo Tables
http://www.candace-tripp.com/download/2table_cascadecombo2k.zipJeffCoachman