function findimg()
{
    var imgs,i;
    // Loop through all images, check if they contain the class roll
    imgs=document.getElementsByTagName('img');
    for(i=0;i<imgs.length;i++)
    {
        if(/dot.gif/.test(imgs[i].src))
        {
            // add the function roll to the parent Element of the image
            imgs[i].parentNode.onmouseover=function(){roll(this);};
            imgs[i].parentNode.onmouseout=function(){roll(this);};
        }
    }
}
function roll(o)
{
    var i,isnode,src,ftype,newsrc,nownode;
    // loop through all childNodes
    for (i=0;i<o.childNodes.length;i++)
    {
        nownode=o.childNodes[i];
        // if the node is an element and an IMG set the variable and exit the loop
        if(nownode.nodeType==1 && /img/i.test(nownode.nodeName))
        {
            isnode=i;
            break;
        }
    }
    // check src and do the rollover
    src = o.childNodes[isnode].src;
    ftype = src.substring(src.lastIndexOf('.'), src.length);
    if(/_on/.test(src))
    {
        newsrc = src.replace('_on','');
    }else{
        newsrc = src.replace(ftype, '_on'+ftype);
    }
    o.childNodes[isnode].src=newsrc;
}

window.onload=function(){
    findimg();
}