dependent select box (example in jquery).html

<select id="country">
  <optoin>Australia</option>
  <option>China</option>
</select>

<select id="city">
</select>


<script>
var cities = {
  "China": ["Hong Kong", "Beijing"],
  "Australia", ["Sydney", "Melbourn"]
}

$('#country').change(function(){
  $('#city').html('')
  
  $.each(cities[this.value], function(city) {
     $('#city').append('<option>' + city +'</optoin>')
  })
})
</script>

gistfile2.txt

<select id="country">
  <optoin>Australia</option>
  <option>China</option>
</select>

<select id="city">
</select>


<script>
var cities = {
  "China": ["Hong Kong", "Beijing"],
  "Australia", ["Sydney", "Melbourn"]
}

$('country').observe('change', function(){
  $('city').setHtml('');
  
  cities[this.value].each(function(city) {
     $('city').append(new Element('option', text: city))
  })
})
</script>

<optoin>Australia</option> is <option>Australia</option>