js触发添加的内容如何插入到freetextbox里面？

<a href="javascript:InsertImage('01','95.gif')"><img src="../images/01/95.gif" border="0"></a> <script language="JavaScript" type="text/JavaScript">
function InsertImage(Folder,URL)
{
parent.Content_editor.document.body.innerHTML= parent.Content_editor.document.body.innerHTML + "<img src=images/" + Folder + "/" + URL + ">"; }
</script>比如我要将原先这段js的同样效果用到freetextbox.应该怎么做？