function imgover(whichimg) {
	var imgsrc = new String(whichimg.src);
	imgsrc = imgsrc.replace(new RegExp('_off\.','g'),'_on\.');
	whichimg.src = imgsrc;
}

function imgout(whichimg) {
	var imgsrc = new String(whichimg.src);
	imgsrc = imgsrc.replace(new RegExp('_on\.','g'),'_off\.');
	whichimg.src = imgsrc;
}

function navrollon(whichimg) {
	var now = new Date();
	var imgsrc = new String(whichimg.src);
	imgsrc = imgsrc.replace(new RegExp('_off\.','g'),'_on\.');
	whichimg.src = imgsrc + '?' + now.getTime();
}

function navrolloff(whichimg) {
	var imgsrc = new String(whichimg.src);
	qindex = imgsrc.indexOf('?');
	if (qindex != -1) {
		imgsrc = imgsrc.substring(0, qindex);	
	}
	imgsrc = imgsrc.replace(new RegExp('_on\.','g'),'_off\.');
	whichimg.src = imgsrc;
}