[monolithed]

А вообще так делать не нужно!

<div class="class1"></div>
<style type="text/css">
div{width: 100px; height: 100px;}
.class1 {background: #000000;}
.class2 {background: #8000FF;}
</style>

<script type="text/javascript">
window.onload = function(){
    if(!/IE(6).+Win/.test(navigator.userAgent)){
        var input = document.getElementsByTagName('div')[0];
        var items = ["mouseover", "mouseout"];
        for (var i = 0; i < items.length; i++){
            (function(){
                var item = items[i];
                input['on'+item] = function(){
                    this.className = (this.className == 'class2') ? 'class1' : 'class2';
                };
            })();
        }
    }
};

</script>