Event.observe(window, 'load', loadHoverOvers, false);

function buttonMouseOver()
{
    var over = this.getAttribute("hoverOver")
    var out = this.getAttribute("hoverOut")
    this.src = this.src.replace(out, over);
}

function buttonMouseOut()
{
    var over = this.getAttribute("hoverOver")
    var out = this.getAttribute("hoverOut")
    this.src = this.src.replace(over, out);
}

function loadHoverOvers()
{
    var buttons = document.getElementsByClassName("iesHover");
    buttons.each(function(button) 
    {
        button.onmouseover = buttonMouseOver;
        button.onmouseout = buttonMouseOut;

        var pic = new Image(100,25); 
        var over = button.getAttribute("hoverOver")
        var out = button.getAttribute("hoverOut")        
        pic.src = button.src.replace(out, over);
    });
}