espero que sea lo que querías...
Código:
<script type="text/javascript" language="JavaScript">
if (document.captureEvents) document.captureEvents(Event.KEYPRESS);
function salta(sChar){
location.href = "#" + sChar;
}
function tomartecla(e){
var codigo;
if (!e) var e = window.event;
if (e.keyCode) codigo = e.keyCode;
else if (e.which) codigo = e.which;
var caracter = String.fromCharCode(codigo);
if (caracter == "a") salta("a");
if (caracter == "b") salta("b");
}
document.onkeypress = tomartecla;
</script>
Saludos