Hide/Show checkbox elements based on select box - Javascript

I have code that enables select list 1 to populate select list 2 as
taken from a railscast. I want to change the select list 2 to a series
of check boxes. I'm not a Javascript person so changing this is making
a mess.

This is the 2 select list code in Javascript:

function countrySelected() {
  country_id = $('fips_code_country_code').getValue();
  options = $('fips_code_state_code').options;
  options.length = 1;
  counties.each(function(state) {
    if (state[0] == country_id) {
      options[options.length] = new Option(state[1], state[2]);
  if (options.length == 1) {
  } else {

Any thoughts on how I can convert this so that the only states displayed
in the checkbox list are those associated with the selected country? Do
I do something with the id element? I think that I need to change line
3 so that it's not looking at the <option>, but rather an id. But
again, I have no clue what I'm doing.

Any help would be GREATLY appreciated.