Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>pruebas</title>
<script language="javascript" type="text/javascript" src="/tinymce/jscripts/tiny_mce/tiny_mce.js"></script>
<script language="javascript" type="text/javascript">
tinyMCE.init({
mode : "textareas",
theme : "simple"
});
</script>
</head>
<body>
<form method="post" name="tinymce">
<textarea name="texto" cols="50" rows="15"></textarea>
</form>
</body>
</html>