function rollover(imgObj) {
	var oldSrc = imgObj.src;
	var ext = oldSrc.substring(oldSrc.lastIndexOf("."), oldSrc.length);
	imgObj.src = oldSrc.substring(0, oldSrc.lastIndexOf(".")) + "_over" + ext;
	if (!imgObj.onmouseout) {
		imgObj.onmouseout = function() {
			rolloff(imgObj);
		}
	}
}

function rolloff(imgObj) {
	var oldSrc = imgObj.src;
	var ext = oldSrc.substring(oldSrc.lastIndexOf("."), oldSrc.length);
	imgObj.src = oldSrc.substring(0, oldSrc.lastIndexOf("_")) + ext;
}