function rollover(myImage) {
	myImageSrc = myImage.src;
	var myPattern = re = /(.*\/)(\w+)_[^\.]+(\..+)$/g;
	if (myImageSrc.indexOf('_off.') != -1) {
		myImage.src = myImageSrc.replace(myPattern, "$1$2_on$3");
	} else {
		myImage.src = myImageSrc.replace(myPattern, "$1$2_off$3");
	}
}