var disabled=false;

function imgOn(Img)
{
    var newSrc=new String(Img);
	if(!disabled) newSrc=newSrc.replace(".gif", "_o.gif");

	return newSrc;
}

function imgOff(Img)
{
    var newSrc=new String(Img);
	if(!disabled) newSrc=newSrc.replace("_o.gif", ".gif");

	return newSrc;
}