ns4 = (document.layers)? true:false
ie4 = (document.all)? true:false

var currentHeader = 3;
var newHeader;
function changeHeader(newHeader) {

	var activeHeader = new Array('graphs/images/top_week_f1.gif','graphs/images/top_month_f1.gif','graphs/images/top_4m_f1.gif','graphs/images/top_year_f1.gif');
	var passiveHeader = new Array('graphs/images/top_week_f2.gif','graphs/images/top_month_f2.gif','graphs/images/top_4m_f2.gif','graphs/images/top_year_f2.gif');

	if (ns4) {
		document.images['h' + currentHeader].src=activeHeader[currentHeader];
		currentHeader = newHeader;
		document.images['h' + newHeader].src=passiveHeader[newHeader];
	} else if (ie4) {
		document.getElementById('h' + currentHeader).src=activeHeader[currentHeader];
		currentHeader = newHeader;
		document.getElementById('h' + newHeader).src=passiveHeader[newHeader];
	}
}

function layerWrite( id, nestref, img, w, h ) {
	if ( (w > 0) && (h > 0) ) {
		wh_str = ' width="' + w + '" height="' + h + '"';
	} else {
		wh_str = '';
	}

	if (ns4) {
		var lyr = (nestref)? eval('document.'+nestref+'.document.'+id+'.document') : document.layers[id].document
		lyr.open();
		lyr.write('<img src=' + img + wh_str + '>');
		lyr.close();
	} else if (ie4) {
		document.all[id].innerHTML = '<img src=' + img + wh_str + '>';
	}
}