How to navigate with keyboard through <ul> <li> element

Question

Possible Duplicate:
KeyBoard Navigation for menu using jquery

I created a menu using <ul> <li> tags and showing it to the user when he presses Enter key in the textbox. He can select items of the menu (navigate in menu) using mouse but I want also to allow him to select items from that menu using up/dow buttons of the keyboard for example.

Is it any way to do that using jQuery or CSS?

My menu has following structure:

<div class="services">
  <div class="items">
    <ul>                           
        <li class="mail-icon"><a href="#" id="mail"><?php echo $langmsg['mail']; ?></a></li>
        <li class="forum-icon"><a href="#" id="forum"><?php echo $langmsg['forum']; ?></a></li>
        <li class="chat-icon"><a href="#" id="chat"><?php echo $langmsg['chat']; ?></a></li>
    </ul>
  </div>
</div>

Note: <li> element has a background image also.

Answer 1

Working jsFiddle

Here is how to handle circular selection:

if (e.keyCode == 38) { // up
    var selected = $(".selected");
    $(".services li").removeClass("selected");

    // if there is no element before the selected one, we select the last one
    if (selected.prev().length == 0) {
        selected.siblings().last().addClass("selected");
    } else { // otherwise we just select the next one
        selected.prev().addClass("selected");
    }
}

css:

.services li.selected {
    background-color: grey;   
}