New to jquery - please help

New to jquery - please help

Ok so Im pretty new to jquery. I was wondering if someone could tell me what im doing wrong with this simple drop down menu code:

<script src="jquery-1.4.2.min.js" type="text/javascript"></script>
<script type="text/javascript">
    $(function() {           
        $('#nav a').onmouseover(function() {
        $('#nav .subMenu').show('2000');
        });
       
        $('#nav a').onmouseout(function() {
        $('#nav .subMenu').hide('2000');
        });     
</script>   

<div id="nav">
    <ul>
        <li><a href="index.html"><img src="images/homeBtn.gif" alt="Home"/></a>
            <div class="subMenu">Return to the home page.</div></li>
        <li><a href="index.html"><img src="images/aboutBtn.gif" alt="Home"/></a></li>

ETC...

CSS:

.subMenu {
        background-color:#00FF00;
        width:50px;
        height:50px;
        display:none;   
    }


The only thing I can think of that different is those script tags are not in the header - which i didnt think was necessary (or is it?)

Cheers