Here is an update that should work for you using window.open:
<form method="post">
<input type="RADIO" name="button" value="http://www.google.com" checked>this button goes to index1.html (Default)
<BR>
<input type="RADIO" name="button" value="http://www.yahoo.com">this button goes to index2.html
<BR>
<input type="RADIO" name="button" value="http://www.stackoverflow.com">this button goes to index3.html
<BR>
<input type="submit" value="Continue">
</form>
<script>
$(function () {
$("form").submit(function (e) {
e.preventDefault();
var url = $(this).find('input[type="radio"]:checked').val();
window.open(url);
});
});
</script>