Sorry, but you're not going to do that with Wizards; it's going to take some VBA code! The concept is usually referred to as "cascading comboboxes," where a second Combobox is populated depending on the selection from the first Combobox In this case, instead of basing the Combobox's RowSource on the selection from the Combobox, you'd base the RecordSource of the Form on it. Here are a couple of links with examples:
http://www.fontstuff.com/access/acctut10.htm
http://bytes.com/forum/thread605958.html
If you Google the term "Cascading Comboboxes" along with "MS Access" you'll probably get a gazillion hits!
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007