The dropdown list you are referring to is something you need Javascript for.
go to www.alaskamfg.net. Click on link at top for "Company Registration", and then click the link md-page that says, "Register as an alaska company"
The form you see has an awesome dropdown list 8 items down. change it and see what happens to list 9. I wrote this one.
Actually, I got it from javascript.internet.com.
The trick is not only having the list tiems do this, BUT to also have the right combo of lists show, AND the right item selected, if you're presenting a record from the database. good luck and happy learning.
Sam