SELECT OPTION a TEXT AREA

[Bellenger]

Hola...

Código HTML:

<script type="text/javascript">
  function coloca(texto,idText){
    document.getElementById(idText).value=texto
  }
</script>
  <select name='combo' onchange=coloca(this[this.selectedIndex].text,'cajita')>
   <option value="peru">PERU</option>
   <option value="japon">JAPON</option>
  </select>
  <input type='text' name='cajita' id='cajita' /> 

Con eso basta...