[PeaceCoder]

<div name="smdf_dropdown_Country[0]" style="display: block;">
  <select name="Country[0]" class="input_select">
    <option selected="selected" value="">Выберите</option>
    <option value="UK">UK</option>
  </select><br/>
  <a onclick="ShowInput('Country[0]')" href="javascript:void(0);">input my own</a>
</div>
<div style="display: block;" name="smdf_input_Country[0]">
  <input class="input_text" type="text" name="Country[0]"/><br/>
  <a onclick="HideInput('Country[0]')" href="javascript:void(0);">select from a list</a>
</div>

function ShowInput(sName) {
  $("[name='smdf_dropdown_"+sName+"']").slideUp();
  $("[name='smdf_input_"+sName+"']").slideDown();
  $("[name='"+sName+"']").val('');
  $("[name='"+sName+"']").change();
 
  $("[name='"+sName+"']").attr('name', 'dhidden_'+sName);
  $("[name='ihidden_"+sName+"']").attr('name', sName);
}

function HideInput(sName) {
  $("[name='smdf_input_"+sName+"']").slideUp();
  $("[name='smdf_dropdown_"+sName+"']").slideDown();
  $("[name='"+sName+"']").val('');

  $("[name='"+sName+"']").attr('name', 'ihidden_'+sName);
  $("[name='dhidden_"+sName+"']").attr('name', sName);
}

Используется jQuery. Вытащил из страницы...