// cross-browser element finding by ID
function getElement(id)
{
    if(document.getElementById)
        x = document.getElementById(id);
    else if(document.all)
        x = document.all[id];
    else if(document.layers)
        x = document.layers[id];

    return x;
}

function rollOn(id)
{
	var img = getElement(id);
	img.src = "images/nav-hover/" + id + ".gif";
}

function rollOff(id)
{
	var img = getElement(id);
	img.src = "images/nav/" + id + ".gif";
}