function rollover(selection)
{
	// preload
	var image = new Image();
	image.src = $(selection).attr("src").replace("-off", "-on");
	
	$(selection).mouseover(function()
	{
		$(this).attr("src", $(this).attr("src").replace("-off", "-on"));
	});
	
	$(selection).mouseout(function()
	{
		$(this).attr("src", $(this).attr("src").replace("-on", "-off"));
	});
}