function roll(img_name1, img_src1, img_name2, img_src2)
	    {
	    document[img_name1].src = img_src1;
	    document[img_name2].src = img_src2;
	    }
		var image1 = new Image();
		image1.src = "images/btn_home_on.jpg";
		var image2 = new Image();
		image2.src = "images/btn_home_off.jpg";
		var image3 = new Image();
		image3.src = "images/btn_portfolio_on.jpg";
		var image4 = new Image();
		image4.src = "images/btn_portfolio_off.jpg";
		var image5 = new Image();
		image5.src = "images/btn_contact_on.jpg";
		var image6 = new Image();
		image5.src = "images/btn_contact_off.jpg";