** in javascript file
function onTypeChange()
{
    alert($('type_id').selectedIndex);
    if ($('type_id').selectedIndex != 0)
    {
        Element.update('chosenType', this.options[this.selectedIndex].text);
        Form.Element.enable('go_button');
    } else {
        Element.update('chosenType', 'Selected Type');
        Form.Element.disable('go_button');
    }
}

** in html
<select class="hosp_select_buttons selectbox" id="type_id" name="type[id]"
        onchange="onTypeChange();">
<option value="">Please select</option>
<option value="1594">Ambulatory Surgical Center</option>
<option value="1595">Birthing Center</option>
<option value="1596">Comprehensive Outpatient Rehabilitation Facilities</option>
<option value="1597">Drug Abuse Treatment Program</option>
<option value="1598">Mammography</option>
<option value="1599">Narcotic Treatment Program</option>
<option value="1600">Outpatient Physical Therapy</option>
<option value="1601">Private Home Care Provider</option></select>