function mouseOver(sender)
{
    var target;
    if(sender) target = sender.target;
    else target = window.event.srcElement;
    
    var url = target.src;
    var newUrl = url.replace(".png", "_on.png");
    target.src = newUrl;
}

function mouseOut(sender)
{
    var target;
    if(sender) target = sender.target;
    else target = window.event.srcElement;
    
    var url = target.src;
    var newUrl = url.replace("_on.png", ".png");
    target.src = newUrl;
}

var preloaded = {} // Store preloaded images in a global array so 
                   // the garbage collector leaves them alone

function preload( url )
{
    var img = new Image();
    img.src = url;
    preloaded[url] = img;
}

function mInitNav( navRoot )
{
    var imgs = navRoot.getElementsByTagName('IMG');
    for(x=0; x<imgs.length; x++)
    {
        var img = imgs[x];
        if(img.className.indexOf('rollover') != -1)
        {
            preload(img.src.replace('.png',"_on.png"));
            
        
            img.onmouseover = mouseOver;
            img.onmouseout  = mouseOut;
        }
        
    }
}