imgOn=new Image();
imgOn.src="images/mt_selected.gif";
imgOff=new Image();
imgOff.src="images/mt_normal.gif";

function tabOn(imgName) {
  if(document.images) {
	  document.images[imgName].src = imgOn.src;
	}
	return true
}

function tabOff(imgName) {
	if(document.images) { 
	  document.images[imgName].src = imgOff.src;
	}
}