Код.

<script language="JavaScript">
<!--
var key = new Array();
key['a'] = "index.htm";
key['b'] = "index1.htm";
key['c'] = "index2.htm";
key['d'] = "index3.htm";
function getKey(keyStroke) {
isNetscape=(document.layers);
eventChooser = (isNetscape) ? keyStroke.which : event.keyCode;
which = String.fromCharCode(eventChooser).toLowerCase();
for (var i in key) if (which == i) window.location = key[i];}
document.onkeypress = getKey;
//-->
</script>