// preset seitch that will alternate between +1 and -1
imageSwitch = 1;

// FUNCTION: imageSwap - exchange one image for another
function imageSwap(imageName,imageA,imageB) {
	if (imageSwitch > 0) {
		document.images[imageName].src = imageA;
	} else {
		document.images[imageName].src = imageB;
	}
	imageSwitch = imageSwitch * (-1);
}