[Deff]

Чо нидь типо так:

<style type="text/css">#txtpastebr{width: 100%;white-space:nowrap;}</style>
<script type="text/javascript" src="http://yandex.st/jquery/1.4.4/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var First=true;
var Sel = $("#brselect");
var Tarea =$("#txtpastebr");
var opt='Ваш выбор,- General,- Mitsubishi,- Clint';
opt = opt.split(',');

 Sel.change(function () {
    var str=$(this).find('option:selected').val();
    var txt=Tarea.val(),a=String.fromCharCode(173); //160
    if(str!=''||str!=opt[0]){
	if(First){First=false;Tarea.val(txt+' '+a+str+a+' ');
	} else {
	  var pattern = a+'('+opt[1]+'|'+opt[2]+'|'+opt[3]+')'+a;
	  var regexp  = new RegExp(pattern,"ig");
	  var txt2=txt.replace(regexp,a+str+a);
	  if(txt2!=txt){Tarea.val(txt2)}else{Tarea.val(txt+' '+a+str+a+' ')}
        }
    }
 });


});
</script>
<form>
  <select id="brselect" name="cat">
     <option selected disable>Ваш выбор</option>
     <option value="- General">- General</option>
     <option value="- Mitsubishi">- Mitsubishi</option>
     <option value="- Clint">- Clint</option>
  </select><br>

  <textarea id="txtpastebr" name="req_message" rows="14"></textarea> 
</form>