This Microsoft Visual How-To walks through a solution to a very common scenario: make the available choices in one combo box depend on the selection made in another combo box.
There are many really good posts on this subject around the Internet- what struck me about this one is that, because of the addition of video content it might apeal to somone tackling this for the first time.
- Candace Tripp's cascading combo box examples. This example uses a similar technique to the Microsoft example, and is one of the most often cited sources for the dependent combo box example.
- Microsoft Access Dependent Drop Down List Box from Blue Claw database Design. This article documents a simpler, though more limited, approach that uses only one line of VBA, relying instead on the query to do the work.