Dependant dropdwn menus and mysql/php

Hi, iam looking for a dependant dropdown menu script that i can use to search a php/mysql page via a url string. I want a three tier menu that the user can select an option and search at any stage . The menus will be region, county and beach a user may want to search for all the beaches in a specific county so would select region which would refresh county to ones within that region they would then select a county and press search. i want it to send just one parameter which in the case would be county= . If they just selected a region and pressed search then region= and if they went through all the menus to a specific beach then beach= .
the only scripts i can find send all three region=&county=&beach= the search page therefore returns all the records in that region which negates the county and beach part. Please help, your help will be much apreciated.