Pon la frase que quieras al revés con solo insertar este script entre <body> y </body>:
<script language="JavaScript">
<!-- This stops non-java browsers from going MAD
var message1="Escribe aquí el texto que quieras,... ¡APARECERÁ AL REVÉS!";
var before = "<font color=black>";
// You put the tags you want before the text here.
var after = "</font>";
// you put the closing tags here.
var message2="";
for (count=message1.length; count >= 0; count--)
message2+=message1.substring(count,count-1);
document.write (before,message2,after);
// -->
</script>