function swapLyrs (lyr1, lyr2) {
	toggleVisibility(lyr1,'block');
	toggleVisibility(lyr2,'none');
	return true;
}
function toggleVisibility(id, vis) {
    if (document.getElementById) {
        eval("document.getElementById(id).style.display = \"" + vis + "\"");
    } else {
        if (document.layers) {
            document.layers[id].display = vis;
        } else {
            if (document.all) {
                eval("document.all." + id + ".style.display = \"" + vis + "\"");
            }
        }
    }
}