Using answers to this question, I have been able to populate a select box based on the selection of another select box. ( I posted my answer here) Pulling the data from an a
You should take a look here for select box manipulation. For what you want, i think JSON will do the right job for you. Anyhow, if i were you, i will do this way: When I change first select, i do an ajax request. With ajax response, i will populate the second box. Same for second box and there you have the third box populated with right data.